We acknowledge the support to the research provided by the laboratory staff of the Sheridan Chemical and Environmental Laboratories, in particular Jaspreet Chandla, Nausheen Zehra, Mike Ovas, Erin Sutton, and Daniel Liao. E.G. is also thankful to Associate Deans Terry Davison and Dave Wackerlin for hosting him at Sheridan. The financial support from Terry Davison and Dr. Iain McNab, Dean of the Faculty of Applied Science and Technology at Sheridan, is also appreciated. ATS Scientific Inc., Quantachrome Instruments, and Malvern Instruments were gracious in assisting with nitrogen adsorption and particle size analyses.

1. Calcium Extraction from Blast Furnace Slag
NOTE: Due to the detrimental effect of acidity on leaching selectivity, the extraction of calcium takes place in two steps, using half the molarity of acetic acid (CH3COOH) that would be used in a single step.
<ol>
	<li>Grind the BF slag using a mortar and pestle and sieve it to particle size below 2 mm.</li>
	<li>Unseal an autoclave reactor that is equipped with a dual-impeller stirrer, a heating/cooling jacket, a pressure gauge, and a thermocouple. Make sure that the interior of the reactor vessel and the components protruding from the reactor head (stirrer shaft; impeller; and thermocouple well, which acts as a baffle) are clean and free of any impurities that may interfere with the calcium extraction process. If they are not, wash them thoroughly.</li>
	<li>Weigh 100 g of the sieved BF slag (&#60;2 mm) and place it in the vessel. Add 731 mL of CH3COOH (2 M) to the vessel and seal it. Make sure that the sealed reactor is properly fastened to its support.</li>
	<li>Place the heating jacket in the proper position, so that it covers almost the whole vessel. Set the heating temperature to 30 &#176;C and start mixing the slurry at 1,000 rpm. Wait until the temperature at the interior of the reactor reaches the set point (approximately 15 min), and then leave the slurry to mix at the aforementioned conditions for 60 min.</li>
	<li>Once the acid extraction time has elapsed, remove the heating jacket, unseal the reactor, and pour the slurry from the reactor into a beaker. A drain valve can also be used, but the coarse solids may block the passage.</li>
	<li>Vacuum-filter the slurry to separate the leachate solution from the residual solids; use filter paper with pore size of 8 &#181;m or less. Process the solids immediately (wet cake), or leave them to dry at ambient temperature for processing at a later time. 
	NOTE: The leachate can be stored at ambient temperature, but it should preferably be further processed (purified and carbonated) shortly afterwards to avoid the uncontrolled precipitation of dissolved compounds.</li>
	<li>Wash both the reactor head and the vessel with DI water to make sure that no residue from the acid or the slag is left behind.</li>
	<li>Place the dry, solid residue from the first Ca extraction step in the vessel and add 731 mL of CH3COOH (2 M). Repeat the same procedure (step 1.5) to mix the solids with the acid (at 30 &#176;C and 1,000 rpm for 60 min).</li>
	<li>At the end of the second extraction step, place the post-extraction slurry into centrifuge tubes. Use large-capacity tubes (e.g., 50 mL or greater) and follow standard centrifugation practices, such as ensuring equal weight in each tube.
	<ol>
		<li>Separate the solids from the leachate by centrifuging the slurry at 2,500 x g for a minimum of 10 min. Slowly pour the supernatant into a new bottle while keeping the solids in the tubes. 
		NOTE: The separation of the solids (suspended silica and residual BF slag) from the calcium acetate-rich liquid phase is thus achieved.</li>
	</ol>
	</li>
	<li>Recover the solid residue resulting from the second extraction step from the tubes and re-suspend them in DI water. Perform another round of centrifugation to remove residual soluble acetates. Recover the washed solids and allow them to dry under ambient conditions.</li>
	<li>Combine the solutions from both the first extraction filtration (filtrate) and the second extraction centrifugation (supernatant) to obtain the post-extraction leachate.</li>
</ol>
2. Physico-chemical Purification of the Post-extraction Leachate
NOTE: Despite the separation of solids from the leachate solution (step 1.9), the resulting supernatant still contains soluble or colloidal impurities. The most important of these impurities are silica, magnesium, and aluminum. According to previously published work32, silica solubility in pure water is proportional to the temperature of the solution (i.e., by decreasing the temperature of pure water, the solubility of silica also decreases). Although the leachate solution is not pure water, it has been found that subjecting the supernatant from the solid-liquid separation of the post-extraction slurry to cooling results in further silica removal (compared to centrifugation alone)2. On the other hand, magnesium and aluminum impurities are present in the supernatant in the form of acetates. In order to significantly reduce their solubility, they must be transformed to insoluble metal hydroxides by pH adjustment2.
<ol>
	<li>Add concentrated NaOH solution (50% w/w) to the supernatant, such that the final concentration of NaOH in the supernatant is 1.25 M; this will increase the pH to around 8.4, thus converting the magnesium and aluminum acetates to their significantly less soluble form of hydroxides. Add the caustic solution slowly while stirring and measuring the pH.</li>
	<li>Place the NaOH-enriched supernatant in the refrigerator and cool it down to 1 &#176;C to cause the extra precipitation of silica.</li>
	<li>Once cooled, vacuum filter the solution using filter paper with a pore size of 0.45 &#181;m. The micro-filtration of the solution results in the further removal of silicon and of the precipitated impurities of magnesium and aluminum.</li>
</ol>
3. Carbonation of the Purified Leachate
NOTE: Due to the regeneration of acetic acid upon carbonation, NaOH is used as an additive to buffer the acidity, which inhibits calcium precipitation. For the production of a purer PCC, NaOH should be used in a sub-equimolar concentration with respect to that of the CH3COOH used in the extraction step (2 M).
<ol>
	<li>Pour the purified leachate into the autoclave reactor. Check both its vessel and cap components to verify that they are clean of residue from previous uses in order to avoid impurities interfering with the carbonation reactions. Add concentrated NaOH (50% w/w) to the vessel, such that the final NaOH concentration in the purified leachate solution is 1.7 M, in order to neutralize the regenerated CH3COOH during carbonation. Seal the reactor and carefully fasten it to its support.</li>
	<li>Place the heating jacket of the reactor in the proper position. Adjust the heating temperature to 30 &#176;C and start mixing the slurry at 1,000 rpm. Wait until the interior of the reactor reaches the desired temperature (approximately 15 min). Start the carbonation of the mixture by introducing to the reactor CO2 of high purity (99.5%) at 2 bar; run for 60 min.</li>
	<li>At the completion of carbonation, remove the heating jacket, depressurize and unseal the reactor, and pour the carbonated slurry into a beaker. 
	NOTE: A drain valve can also be used after depressurization, as the solids are fine.</li>
	<li>Vacuum-filter the resulting slurry to separate the solid precipitates from the solution; use filter paper with a pore size of 8 &#181;m or less. Rinse the filter cake thoroughly with DI water under vacuum to remove soluble sodium. 
	NOTE: The marked reduction in the conductivity of the rinse filtrate can be used to confirm the rinse end-point.</li>
	<li>Oven-dry the solid material at 105 &#176;C for 24 h to retrieve the PCC.</li>
</ol>
4. Hydrothermal Conversion of the Extraction Solid Residues
NOTE: For hydrothermal conversion, calcium-depleted residual solids from the blast furnace slag acetic acid extraction were used. After each extraction run (including both steps), less than 50 wt% of the initial mass can be recovered (due to calcium extraction and the partial loss of colloidal silica in filtration and depending on the filter paper porosity used). Thus, multiple batches of extraction are needed to generate the mass of solids used in the hydrothermal conversion step.
<ol>
	<li>Place 60 g of the dry, residual solids from the calcium extraction into a clean autoclave reactor. Add 300 mL of 2 M NaOH solution. Seal the reactor and fasten it to its support.</li>
	<li>Place the heating jacket of the reactor in the proper position. Adjust the heating temperature to 150 &#176;C and start mixing the slurry at 300 rpm. Wait for approximately 45-50 min, until the interior of the reactor reaches the desired temperature. Leave the slurry to mix at the aforementioned conditions for 24 h.</li>
	<li>At the completion of the hydrothermal conversion, remove the heating jacket and allow the reactor to cool down for 60 min, to approximately 35 &#176;C. The reactor jacket&#39;s cooling circuit can also be used to speed cooling.
	<ol>
		<li>Unseal the reactor and pour the converted slurry into a beaker.</li>
	</ol>
	</li>
	<li>Vacuum-filter the slurry to separate the converted solids from the solution; use filter paper with a pore size of 8 &#181;m or less. Rinse the solids thoroughly with DI water under vacuum to remove the excess caustic. 
	NOTE: The marked reduction in conductivity of the rinse filtrate can be used to confirm the rinse end point.</li>
	<li>Oven-dry the filtered material at 105 &#176;C for 24 h to obtain the hydrothermally converted material.</li>
	<li>Disaggregate the granular material using a mortar and pestle and sieve the resulting material to a particle size &#60;0.85 mm.</li>
</ol>
5. Heavy Metal Adsorption Tests with the Zeolitic Product
NOTE: Ni2+ is selected as the heavy metal for investigation. Contaminated solutions with different initial heavy metal concentrations were synthesized. Initial heavy metal concentrations of 2-200 mg/L were chosen as appropriate for the needs of the present study.
<ol>
	<li>To prepare the contaminated solutions for the equilibrium experiments, use a micro-pipette to add an appropriate amount of 1,000 mg/L analytical-grade standard solution of Ni2+ into 1 L of ultra-pure water in a volumetric flask to produce solutions of the desired Ni2+ concentrations (2 mg/L, 10 mg/L, 20 mg/L, 100 mg/L, and 200 mg/L).</li>
	<li>In capped plastic bottles, disperse 1 g of the hydrothermally converted material resulting from step 4.6 in 100 mL of each synthetically prepared contaminated solution.</li>
	<li>Add concentrated NaOH (2 M at first and 0.5 M closer to the end point) dropwise to adjust the pH of the solutions to 4-5. Continuously stir the solution at a low speed using a magnetic stirring bar on a stirring plate. Monitor the pH while adding the NaOH by using a pH electrode soaked in the solution.</li>
	<li>Place the bottles in a shaker incubator and agitate them at 160 rpm and 20 &#176;C for 24 h.</li>
	<li>After mixing, add concentrated HCl (2 M at first and 0.2 M closer to the end point) dropwise to the solution to readjust the pH to 4-5. During the adjustment, continuously stir the solution at a low speed using a magnetic stirring bar on a stirring plate. Monitor the pH continuously while adding the HCl by using a pH electrode soaked in the solution.</li>
	<li>Place the slurry in centrifuge tubes. Separate the solids from the solution by using a laboratory centrifuge at 2,500 x g for 5 min. Carefully pour the supernatant solution to a new bottle while keeping the solids in the centrifuge tube.</li>
	<li>Acidify the solution with HNO3 (2 wt% nitric acid concentration) to reduce the pH to &#60;2. 
	NOTE: This step is performed to ensure that the ions remain in solution during storage (at ambient temperature) prior to further manipulation and analysis.</li>
	<li>Determine the equilibrium concentration of the investigated heavy metal in the supernatant by using ICP-OES. 
	NOTE: Solutions are diluted by a factor of 10-100x using 2 wt% HNO3 diluent, such that the expected concentration falls in the linear range of the instrument calibration (0-2 mg/L). Yttrium, at 2 mg/L, is added to each diluted sample as an internal standard. The ICP-OES instrument is operated based on the manufacturer&#39;s recommendations for the analysis of metals in wastewaters37. Alternate techniques for the determination of nickel concentration in solution, such as ICP-MS and AAS, are also suitable for this step.</li>
	<li>Calculate the amount of heavy metal adsorbed per g of the adsorbent at equilibrium (qe) using the following formula: 
	<img alt="Equation" src="/files/ftp_upload/55062/55062eq1.jpg" /> 
	where Co is the initial concentration (&#181;mol/mL) of the heavy metal ions in the solution, Ce is the equilibrium concentration of the heavy metal ions in the solution (&#181;mol/mL), V is the volume of the contaminated solution (mL), and m is the mass of the dry adsorbent (g).</li>
</ol>

We have nothing to disclose.

Although the indirect carbonation7,8 and the hydrothermal conversion9,10 of BF slags have been widely researched as separate processes, their coupling for the symbiotic synthesis of PCC and zeolitic minerals has only recently been proposed5, and the methodology is herein presented in detail. The most critical step of the process is the sufficient (almost total) extraction of Ca and the limited leaching of silica and aluminum from the BF slag during the extraction phase. The high amount of calcium in the leachate secures a high rate of PCC synthesis after carbonation and inhibits the generation of large amounts of undesired phases (e.g., tobermorite, hydrogarnet (Ca3Al2(SiO4)3-y(OH)4y)) among the hydrothermally converted products9. On the other hand, the preservation of the greatest part of Si and Al in the post-extraction solid residues is of instrumental importance for the formation of zeolitic minerals.
To this end, among the several extractants investigated in the literature7,8,10,11,34,35,36, acetic acid was selected as the most suitable for the aim of this study. The particular extraction agent causes the release of high amounts of calcium from the slag to the solution, while ensuring the retention of the largest part of Si and Al in the resulting residues. This promotes the parallel formation of PCC and zeolites. The acetic acid-to-calcium molar ratio used in each extraction step was 2:1 (based on the mass of slag, the calcium content of the slag, and the volume of acetic acid solution), meaning that the total ratio over two extraction steps was 4:1. Since calcium acetate has an acetate-to-calcium ratio of 2:1, double the stoichiometric amount was used, as was found necessary by Chiang et al.5
In order to limit the presence of undesired impurities in the generated PCC, the leachate solution should be subjected to further purification before being carbonated; this is another novelty of the proposed symbiotic process. In earlier work, the PCC quality (chemical purity, mineral composition, particle size and shape) was negatively affected by impurities. For the synthesized PCC to be qualified as paper filler, certain criteria must be met. The produced PCC should be characterized by high chemical purity (min. 98 wt% Ca), homogenous mineralogical structure, small average particle size, and narrow size distribution6. As presented in the Representative Results section, the proposed process affords these characteristics. The precipitated carbonate is of high purity and has a calcium content of 98.1 wt% (Figure 2a).
The optimization of the hydrothermal conversion process resulted in the production of a material with the ability to act as a heavy metal adsorbent. The optimization was made by finding the most suitable combination of temperature, NaOH concentration, and reaction time. Tobermorite is one of the undesirable mineral phases that can form; its layered crystal structure leads to reduced specific surface area39, a trait important for sorbents, though it has been reported that tobermorite can act as a sorbent through an ion-exchange mechanism40. Nonetheless, the mineral phase that dominates the converted material in this study, under optimal conditions, is that of analcime (Figure 3b). It is a zeolite that has been reported to have a notable heavy metal adsorption capacity41,42 and can thus be used for the removal of toxic contaminants from wastewaters, as shown herein.
The potential use of this material as a sorbent was investigated for nickel removal from water. The pH levels of the synthetically prepared contaminated solutions of Ni2+ were controlled to 4-5 during the test, first, to prevent dissolution of the material in the initial acidic environment of the synthetic solution, and, second, to adjust the pH to the level typically found in heavy metal remediation conditions43. Three different isotherm models, namely Langmuir, Freundlich, and Temkin, were applied in order to characterize the adsorption processes (Figures 4 and 5), with the Langmuir model proving to be the most appropriate. It should be noted that the Dm values attributed to the unadjusted equilibrium adsorbent-adsorbate solutions are higher than those corresponding to the equilibrium solutions after the adjustment. This is explained by the rise in pH that takes place during the adsorption reactions occurring in the solution until it reaches its equilibrium. A higher pH (&#62;5) causes nickel to precipitate as Ni(OH)2, according to geochemical modeling and experimental studies by Santos et al.44, which in turn inflates the Dm value. This type of heavy metal should not be accounted as the actual adsorption capacity of the tested material. In an effort to avoid such biased measurements, the pH of the equilibrated adsorbent-adsorbate solution was re-adjusted to ~5.0 by adding drops of concentrated hydrochloric acid. The lower qe values (Figure 4a), and consequently, the more conservative Ni adsorption estimate of the pH-adjusted solution, can thus be obtained.
The techniques described herein have the potential to be adapted to the exploitation of other materials as sources of Ca, Al, and Si for the synthesis of PCC and zeolites. Potential materials other than blast furnace slag can include steelmaking slags, incineration ashes, mining and mineral processing tailings, construction and demolition waste, natural minerals, etc. Not all of these materials contain the same proportions of Ca, Al, and Si as BF slag (which is what makes BF slag particularly attractive), but nonetheless, they can still be used to produce PCC, zeolites, or other mineral-derived products (e.g., aggregates45 or pozzolanic materials) through similar processing techniques (some combination of extraction, precipitation and/or chemical conversion). Also, the zeolitic materials produced from BF slag or other minerals should be tested for other wastewater or remediation applications, as they likely have adsorption capacity for other heavy metals, such as Cd, Pb, and Zn46. Economics (the need to pay for virgin materials versus the avoidance of disposal fees for waste materials, or the financial return on utilizing the products for higher- or lower-value applications) should play a role in the identification of a suitable mineral feedstock. Substitution of other process inputs (acetic acid, sodium hydroxide, and concentrated CO2) by less costly or more easily recoverable alternatives should also be considered to improve processing costs.

The indirect carbonation of industrial residues rich in alkaline metals has been widely researched as part of carbon capture and storage (CCS) technology1,2,3,4. Some amount of CO2 can be stored efficiently, permanently, and in a manner that is benign to the atmosphere. However, while valuable materials are formed, there is a part of the technique that remains inadequately explored. In the indirect carbonation process, calcium is selectively extracted from the material and subsequently subjected to carbonation under controlled conditions. However, the waste valorization process generates solid residues from the material; these residues are not further processed or exploited after the calcium extraction stage. Processing routes that reduce the production of such residues, or even that eliminate them, should be found. To this end, recently, there has been an effort to develop and optimize a process by which, by using blast furnace (BF) slag as the starting material, a zero-waste mineral sequestration of carbon, accompanied with the formation of useful minerals, can be achieved5,6.
Several waste materials are qualified as efficient reactants for CO2 mineralization. Among them, iron- and steel-making slags present considerably higher experimental CO2 uptakes than every other industrial waste4. The attractiveness of BF slag for waste valorization lies in its qualities (chemical, mineral, and morphological properties) and the potential applications of the material5. It is a by-product of the iron-making process, wherein impurities from iron ore are removed in a pyrometallurgical process. Based on the way it is cooled down after its separation from the molten iron, four different types of slag are generated: (i) air-cooled (i.e., crystalline), (ii) granulated (i.e., vitrified), (iii) expanded (i.e., foamed), and (iv) pelletized.
Although the production of precipitated calcium carbonate (PCC) using the indirect carbonation of BF slag is a process that has managed to attract much attention7,8, the hydrothermal conversion of slag for the production of zeolitic minerals is a technology that has been studied and developed only during recent years9,10,11. However, in none of the cases has it been considered as a technique that could be used in combination with the indirect carbonation of BF slag in order to achieve the symbiotic formation of PCC and zeolites. Following the two-way valorization process herein described, these two techniques are coupled to accomplish the sufficient sequestration of CO2 while also obtaining zeolitic minerals and eliminating any potential solid residues. According to this procedure, CO2 is stored in the calcium that was extracted from slag by acid leaching via a mineral carbonation reaction5. To achieve the suitable PCC product properties for applications in papermaking (mineralogy, particle size distribution, and particle morphology), the leachate from the extraction stage is first physico-chemically purified6. In parallel, zeolitic minerals are formed in a caustic solution via the hydrothermal conversion of the solid residues resulting from the calcium extraction stage5.
Zeolite is an alumino-silicate mineral. It occurs naturally, but it can also be industrially produced on a large scale. Numerous unique zeolite frameworks have been identified, leading to various applications for the materials. For example, they can be used as catalysts in several industrial sectors12,13; they are found in detergents and in construction materials as additives in asphalt, concrete14,15, and Portland cement16,17; and they also have applications in the medical18,19,20 and agricultural21,22,23 domains. Furthermore, due to their large specific surface areas and their cation exchange capacities, zeolites can also be used as sorbents24,25,26,27. These particular sorbents can also be used to directly treat heavy metal-laden streams, such as wastewater or contaminated groundwater28,29,30,31. In this study, the zeolitic material produced from BF slag via the two-way valorization process is, for the first time, tested as an adsorbent for a heavy metal, namely, nickel.
For the proposed symbiotic process, an extraction agent amiable to both the PCC and zeolite formation should be used. Thus, the choice of a suitable extractant is critical. Among the several leaching agents applied in prior research on both indirect carbonation7,8 and hydrothermal conversion10,11 of BF slag, acetic acid was selected as the most promising. Hydrochloric acid10 exhibits detrimental effects on both the generation of PCC and on the leaching selectivity, causing significant losses in the quantities of Si and Al in the leachate solution. On the other hand, formic acid11 has proved to be efficient, since it manages to efficiently remove Ca and Mg from the slag while presenting remarkable leaching selectivity, leaving both the Si and the Al undisturbed. However, it presents a lower acid dissociation constant than acetic acid33, suggesting that the precipitation of calcium carbonate should be more readily achievable after the employment of acetate solutions as the extraction agent. It has also been shown that, in some cases, such as with the use of succinates34 and oxalates35, non-carbonate precipitates form in place of PCC. Eloneva et al.36 compared sixteen extractants for calcium removal from steelmaking slags and found acetic acid to be the most efficient (best performance between 0.5 M and 2 M extractant concentrations) and most successful (highest calcium recovery at ~100%).
The following protocol describes in detail the lab-scale experimental process that leads to the formation of high-purity PCC and a zeolitic material, with potential uses as paper fillers and heavy metal sorbents, respectively. BF slag is the starting material. The testing procedures applied for the assessment of the synthesized zeolitic material as an adequate heavy metal sorbent are also outlined.

<table><tbody><tr><td>Acetic acid (CH&lt;sub&gt;3&lt;/sub&gt;COOH)</td><td>Caledon Laboratories</td><td>1000-1-29</td><td>Glacial (&amp;ge;99.7%).</td></tr><tr><td>Autoclave reactor</td><td>Parr</td><td>4525-T-HC-M(HC)</td><td>One liter volume, equipped with dual turbine impeller, baffle and electric heating jacket.</td></tr><tr><td>Blast Furnace (BF) slag</td><td>ArcelorMittal</td><td>-</td><td>Granulated BF Slag from Ghent (Belgium); Pelletized BF Slag from Hamilton (Canada).</td></tr><tr><td>Carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;)</td><td>Praxair</td><td>TBC</td><td>Industrial grade (99.5%).</td></tr><tr><td>Centrifugal Mill</td><td>Retsch</td><td>ZM100</td><td>0.50 mm sieve.</td></tr><tr><td>Centrifuge</td><td>Thermo Electron</td><td>IEC CL30</td><td>To separate solids from liquids.</td></tr><tr><td>Ecoclave reactor</td><td>B&amp;uuml;chi</td><td>Type 3E</td><td>One liter volume, equipped with turbine impeller, baffle and electric heating jacket.</td></tr><tr><td>Filter paper</td><td>Fisher Scientific</td><td>P8 (09-795F)</td><td>Porosity: coarse; flow rate: fast.</td></tr><tr><td>Hydrochloric acid (HCl)</td><td>Caledon Laboratories</td><td>6025-1-29</td><td>Reagent grade (36.5%-38.0%).</td></tr><tr><td>Incubator</td><td>New Brunswick Scientific</td><td>I 24</td><td>Orbital shaker with temperature control.</td></tr><tr><td>Inductively Coupled Plasma Mass Spectrometer (ICP-MS)</td><td>Thermo Electron</td><td>X Series</td><td>To determine the concentration of Al, Ca, Mg and Si in the post-extraction leachates and post-carbonation liquid medium.</td></tr><tr><td>Inductively Coupled Plasma Optical Emissions Spectrometer (ICP-OES)</td><td>PerkinElmer</td><td>Optima 8300</td><td>To determine the concentration of Ni in the post-centrifuged equilibrated adsorbent-adsorbated leachate.</td></tr><tr><td>Laser Diffraction Analysis (LDA)</td><td>Malvern</td><td>Mastersizer 3000</td><td>To measure the average particle size diameter and particle size distribution (PSD) of the solids.</td></tr><tr><td>Microbalance</td><td>Sartorius</td><td>Quintix224-S1</td><td>Four decimals.</td></tr><tr><td>Ni standard solution</td><td>Perkin Elmer</td><td>N9300136</td><td>Concentration of 1,000 mg/1,000 mL.</td></tr><tr><td>Nitric acid (HNO&lt;sub&gt;3&lt;/sub&gt;)</td><td>Caledon Laboratories</td><td>7525-1-29</td><td>Reagent grade (68.0%-70.0%).</td></tr><tr><td>Oven</td><td>Fisher Scientific</td><td>Isotemp oven</td><td>105&amp;deg;C.</td></tr><tr><td>pH meter</td><td>Fisher Scientific</td><td>AB15</td><td>Calibrated with standard solutions before each set of measurements; temperature corrected to 25 &amp;deg;C.</td></tr><tr><td>Sodium hydroxide (NaOH)</td><td>Caledon Laboratories</td><td>7871-6-42</td><td>Reagent grade (50% W/W).</td></tr><tr><td>X-ray Diffraction (XRD)</td><td>Rigaku</td><td>MiniFlex 600</td><td>To characterize mineralogical properties of adsorbant solids.</td></tr><tr><td>X-ray Fluorescence (XRF)</td><td>PANalytical</td><td>Zetium</td><td>To characterize chemical composition of solids.</td></tr><tr><td>Nitrogen Adsorption</td><td>Quantachrome</td><td>NOVAtouch&amp;nbsp;</td><td>To characterize specific surface area, pore volume and mean pore diameter of solids.</td></tr></tbody></table>

two-way valorization of blast furnace slag: synthesis of precipitated calcium carbonate and zeolitic heavy metal adsorbent

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with sufficient heavy metal adsorption capacity. To this end, blast furnace slag, a residue from iron-making, is utilized as the starting material. Calcium is selectively extracted from the slag by leaching with acetic acid (2 M CH3COOH) as the extraction agent. The filtered leachate is subsequently physico-chemically purified and then carbonated to form precipitated calcium carbonate (PCC) of high purity (&lt;2 wt% non-calcium impurities, according to ICP-MS analysis). Sodium hydroxide is added to neutralize the regenerated acetate. The morphological properties of the resulting calcitic PCC are tuned for its potential application as a filler in papermaking. In parallel, the residual solids from the extraction stage are subjected to hydrothermal conversion in a caustic solution (2 M NaOH) that leads to the predominant formation of a particular zeolitic mineral phase (detected by XRD), namely analcime (NaAlSi2O6&#8729;H2O). Based on its ability to adsorb Ni2+, as reported from batch adsorption experiments and ICP-OES analysis, this product can potentially be used in wastewater treatment or for environmental remediation applications.

To test the carbonate precipitates for purity and yield, several instrumental techniques can be applied. The elemental composition (including major and minor components) can be determined either by inductively coupled plasma atomic emission spectroscopy (ICP-OES), by inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectroscopy (AAS) following acid digestion (in HCl), or by X-ray fluorescence spectroscopy (XRF) with the sample in powder or pellet form. XRF is less sensitive for minor components (&#60;1 wt%). More details and examples are found in De Crom et al.6 These results will demonstrate if undesired impurities are present and will help determine, by mass balance, the efficiency of converting the calcium content of the original slag into PCC. The mineral composition is best determined by X-ray powder diffraction (XRD). The resulting diffractogram provides qualitative information about the presence of crystalline mineral phases. Quantification of the relative amounts is made by Rietveld refinement technique (with an accuracy of around &#177; 2-3 wt%). More details and examples can be found in Santos et al.38 These results will verify if the process conditions or impurities affect the crystallization process, generating additional undesired phases besides calcite (CaCO3). Particle size distribution (PSD) and mean particle diameter are best determined by wet (DI water) laser diffraction. More details and examples can be found in De Crom et al.6 These results are used to assess if the PCC meets the requirements of its intended application (i.e., papermaking), which usually specify an upper cut-off size and a span of distribution.
The elemental composition of the post-extraction leachate and post-carbonation products, as well as the XRD pattern and volume-based PSD of the post-carbonation precipitates, are presented in Figures 1 and 2. ICP-MS technique was used to measure the content (wt%) of certain metals (Ca, Mg, Al, and Si) in the composition of the leachate after the Ca extraction stage and before its carbonation. The use of analytical-grade acetic acid (2 M) as the leaching agent resulted in a Ca extraction of approximately 90% (Figure 1a). According to the results, an even higher extraction efficiency was detected for magnesium (almost 100%), another metal that can be efficiently carbonated but under more intensive conditions.
The behavior of silica and aluminum during the extraction stage was also investigated. To successfully produce alumino silicate-based zeolitic minerals through hydrothermal conversion, but also to avoid contamination of the synthesized PCC with undesired elements, both silica and aluminum should remain in the solid phase during the extraction process. According to the results, acetic acid exhibited a satisfactorily limited leaching of silica and aluminum, with almost 92% of silica and 62% of aluminum remaining unaffected during the leaching process (Figure 1b).
The carbonation of the purified leachate solution resulted in the production of PCC with desirable characteristics, as depicted in Figure 2. Based on the XRD diagram (Figure 2b), the mineral phase that was mainly synthesized was that of calcite (88.2 wt%), whereas small quantities of nesquehonite (Mg(HCO3)(OH)&#183;2H2O; 3.2 wt%) and magnesian calcite (Ca1-0.85Mg0-0.15CO3; 2.8 wt%) were also present. From the PSD analysis of the material (Figure 2c), it became clear that the mean particle size was small and the particle size distribution was narrow.
In parallel with carbonation, the solid residues from the extraction stage were subjected to hydrothermal conversion. Characterization of the hydrothermally converted material, to verify the production of the zeolitic minerals and to assess the morphology, was conducted as follows. The elemental composition is most readily obtained by XRF. Trace-element determination requires acid digestion followed by ICP-OES, ICP-MS, or AAS, with the digestion carried out using sequential acid dissolution (HNO3-HF or HNO3-HClO4-HF) to dissolve the silica phase. While there is no specific elemental composition targeted for the converted material, this analysis helps clarify the mineral composition determined by XRD. XRD analysis, to determine mineral composition, the PSD and mean particle diameter were determined similarly to carbonate precipitates, as aforementioned. Specific surface area, pore volume, and mean pore diameter were determined by nitrogen adsorption, with the isotherms interpreted according to Brunauer-Emmett-Teller (BET) multi-point theory. Samples should be initially degassed under vacuum at 350 &#176;C for 4 h. More details and examples can be found in Chiang et al.5
The Ca, Mg, Al, and Si content in the hydrothermally converted material, determined by using the ICP-OES technique, is shown in Figure 3a, whereas their mineralogical composition, determined from XRD patterns, is shown in Figure 3b. The mean particle size and size distribution, obtained from the PSD analysis, is shown in Figure 3c. The resulting material is mineralogically characterized by the presence of two main phases: analcime (NaAlSi2O6&#8729;H2O) and tobermorite (Ca5(OH)2Si6O16&#8729;4H2O). The existence of the latter in the converted extraction residues justifies the notable calcium content (22.5 wt%) that was detected in the chemical composition of the material, as it was analyzed using XRF. Silica (37.2 wt%) and aluminum (11.2 wt%) were the other primary elements, whereas magnesium was present in amounts of approximately 4 wt%. Based on the PSD analysis, the volume moment (De Brouckere) mean particle diameter (D[4,3]) of the converted materials was 86.6 &#181;m, whereas the size distribution ranged from 0.594 &#181;m to 1.11 mm. Nitrogen adsorption analysis confirmed the formation of mesoporous material (46.0 nm mean pore diameter), with the specific surface area and pore volume of the hydrothermally converted material, respectively, increasing from 4.89 m2/g to 95.23 m2/g and from 0.014 mL/g to 0.610 mL/g over the original slag.
The equilibrium adsorption isotherms of Ni2+ onto the hydrothermally converted material, before and after the pH adjustment of the equilibrated adsorbent-adsorbate solution, as well as the fitting of the experimental data to the linearized Langmuir, Freundlich, and Temkin adsorption models are shown in Figure 4.
The Langmuir model is based on some reasonable assumptions that characterize the chemisorption process. According to them, the surface of the adsorbent only offers a fixed number of adsorption sites, with identical shapes and sizes, characterized by identical adsorption capacity. The adsorbed material forms only one layer (thickness of one molecule) on the surface of the adsorbent, and the temperature is constant. Mathematically, the Langmuir model is expressed by the following equation:
<img alt="Equation" src="/files/ftp_upload/55062/55062eq2.jpg" />
where Ce is the equilibrium concentration of adsorbate in solution (&#181;mol/100 mL), qe is the amount of metal adsorbed per g of adsorbent at equilibrium (&#181;mol/g), Dm is the theoretical maximum monolayer coverage capacity of the adsorbent (&#181;mol/g), and k is the Langmuir isotherm constant (100 mL/&#181;mol).
The Freundlich isotherm is not constrained by the assumptions required in the Langmuir model. Instead, it describes the physical adsorption process that can be applied to adsorbents with heterogeneous surfaces. The adsorption sites, distributed all over the adsorbent&#39;s surface, are characterized by different affinities for the adsorbate, whereas the adsorbed material forms more than one layer on the surface of the adsorbent. The Freundlich model is mathematically expressed as:
<img alt="Equation" src="/files/ftp_upload/55062/55062eq3.jpg" />
where Kf and n are the Freundlich isotherm constants, corresponding to adsorption capacity and adsorption intensity, respectively.
Finally, the Temkin model assumes that the adsorption heat of all the molecules of the layer linearly decreases with coverage due to the adsorbent-adsorbate interactions, whereas the binding energies are uniformly distributed. The Temkin model is expressed by the following equation:
<img alt="Equation" src="/files/ftp_upload/55062/55062eq4.jpg" />
where R is the universal gas constant (8.314 J/mol/K), T is the temperature (K), &#916;Q is the variation of adsorption energy ((J/mol)&#8729;(g/&#181;mol)), and K0 is the Temkin isotherm equilibrium binding constant (100 mL/&#181;mol).
The values of the coefficients for all the applied models were calculated based on the plotted adsorption isotherms (Figure 4a) and the linear forms of the Langmuir, Freundlich, and Temkin equations (Figure 4b-4d). The coefficient values, along with the linear equations, are presented in Table 1. Finally, comparisons between the experimental data and the theoretical adsorption isotherms of Ni2+ onto the activated material for the three different adsorption models are presented in Figure 5. Based on the contour of the graphs and the high proximity of the experimental results to the theoretical isotherm curves, it has been verified that the newly formed sorbent material can be effectively used as a Ni2+ adsorbent.
By comparing the fitted results presented in Figure 5a and 5b, as well as the regression coefficients (R2) for the Langmuir and Freundlich models (Table 1), it is clear that the Langmuir equation is the one that better describes the experimental data. This implies that the adsorption of Ni2+ ions on the converted material is a monolayer adsorption and that its nature is that of a chemisorption process. In order to further analyze the nature of the investigated adsorption, we also attempted to fit the Temkin model to the experimental data. From the graph shown in Figure 5c and its high R2 (Table 1), it is clear that the Temkin model also fits the experimental data well. Based on the positive values of the variation of adsorption energy (&#916;Q), it can be concluded that the adsorption is exothermic.
<img alt="Figure 1" src="/files/ftp_upload/55062/55062fig1.jpg" /> 
Figure 1: Acetic acid extraction. Concentration of Al, Ca, Mg, and Si in the leachate solutions (first step, second step, and in total) resulting from the reaction between acetic acid and ground, granulated BF slag at 30 &#176;C, 1,000 rpm and for 60 min. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55062/55062fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55062/55062fig2.jpg" /> 
Figure 2: Calcium carbonate precipitates. (a) Composition of the carbonate precipitate, expressed in weight percentage per element, normalized to 100% total. (b) XRD diagram of the post-carbonation precipitate. (c) Particle size distribution of the post-carbonation precipitate. Reproduced from De Crom et al.6 with permission from Elsevier (3879261230348). <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55062/55062fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55062/55062fig3.jpg" /> 
Figure 3: Hydrothermally converted material. (a) Composition of the hydrothermally converted material, expressed in weight percentage per element, normalized to 100% total. (b) XRD diagram of the hydrothermally converted material. (c) Average particle size distribution of the hydrothermally converted material. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55062/55062fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/55062/55062fig4.jpg" /> 
Figure 4: Adsorption isotherms. (a) Adsorption isotherm data of Ni2+ on the zeolitic material before and after the pH adjustment. (b-d) Fitting of the experimental data to the linearized Langmuir, Freundlich, and Temkin adsorption models. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55062/55062fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/55062/55062fig5.jpg" /> 
Figure 5: Experimental and simulated data proximity. Comparison between the experimental data (exp) and the simulated adsorption isotherms (calc) of Ni2+ onto the zeolitic material according to the (a) Langmuir, (b) Freundlich, and (c) Temkin models. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55062/55062fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td></td>
			<td colspan="2">Linear Equations</td>
			<td>Coefficients</td>
			<td>Unadjusted</td>
			<td>Adjusted</td>
		</tr>
		<tr>
			<td rowspan="3">Langmuir Equation</td>
			<td colspan="2" rowspan="3"><img alt="Equation" src="/files/ftp_upload/55062/55062tableeq1.jpg" /></td>
			<td>Dm</td>
			<td>196.08</td>
			<td>196.08</td>
		</tr>
		<tr>
			<td>k</td>
			<td>0.174</td>
			<td>0.0851</td>
		</tr>
		<tr>
			<td>R2</td>
			<td>0.997</td>
			<td>0.993</td>
		</tr>
		<tr>
			<td rowspan="3">Freundlich Equation</td>
			<td colspan="2" rowspan="3"><img alt="Equation" src="/files/ftp_upload/55062/55062tableeq2.jpg" /></td>
			<td>n</td>
			<td>2.50</td>
			<td>2.13</td>
		</tr>
		<tr>
			<td>Kf</td>
			<td>26.50</td>
			<td>17.64</td>
		</tr>
		<tr>
			<td>R2</td>
			<td>0.840</td>
			<td>0.893</td>
		</tr>
		<tr>
			<td rowspan="3">Temkin Equation</td>
			<td colspan="2" rowspan="3"><img alt="Equation" src="/files/ftp_upload/55062/55062tableeq3.jpg" /></td>
			<td>&#916;Q</td>
			<td>102.30</td>
			<td>93.99</td>
		</tr>
		<tr>
			<td>K0</td>
			<td>9.97</td>
			<td>3.58</td>
		</tr>
		<tr>
			<td>R2</td>
			<td>0.998</td>
			<td>0.978</td>
		</tr>
	</tbody>
</table>
Table 1: Adsorption isotherm parameters for the Ni2+ adsorption onto the zeolitic material. Equations of, and fitted parameters from, linearized Langmuir, Freundlich, and Temkin adsorption models.

Watch this Scientific Journal Video about Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent at JoVE.com

Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

A protocol for the parallel production of precipitated calcium carbonate and zeolitic material from blast furnace slag via mineral carbonation and alkaline hydrothermal conversion, respectively, is presented. The performance of the zeolitic material towards nickel adsorption is tested.

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with ...

two-way-valorization-blast-furnace-slag-synthesis-precipitated

Nanyang Technological University

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12.3K Views.  Cranfield University. A protocol for the parallel production of precipitated calcium carbonate and zeolitic material from blast furnace slag via mineral carbonation and alkaline hydrothermal conversion, respectively, is presented. The performance of the zeolitic material towards nickel adsorption is tested. 

Video: Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

Synthesis and Operation of Fluorescent-core Microcavities for Refractometric Sensing

This paper discusses fluorescent core microcavity-based sensors that can operate in a microfluidic analysis setup. These structures are based on the formation of a fluorescent quantum-dot (QD) coating on the channel surface of a conventional microcapillary. Silicon QDs are especially attractive for this application, owing in part to their negligible toxicity compared to the II-VI and II-VI compound QDs, which are legislatively controlled substances in many countries. While the ensemble emission spectrum is broad and featureless, an Si-QD film on the channel wall of a capillary features a set of sharp, narrow peaks in the fluorescence spectrum, corresponding to the electromagnetic resonances for light trapped within the film. The peak wavelength of these resonances is sensitive to the external medium, thus permitting the device to function as a refractometric sensor in which the QDs never come into physical contact with the analyte. The experimental methods associated with the fabrication of the fluorescent-core microcapillaries are discussed in detail, as well as the analysis methods. Finally, a comparison is made between these structures and the more widely investigated liquid-core optical ring resonators, in terms of microfluidic sensing capabilities.

Fluorescent-core microcavity sensors employ a high-index quantum-dot coating in the channel of silica microcapillaries. Changes in the refractive index of fluids pumped into the capillary channel cause shifts in the microcavity fluorescence spectrum that can be used to analyze the channel medium.

This paper discusses  fluorescent core microcavity-based sensors that can operate in a microfluidic  analysis setup. These structures are based on the ...

Synthesis and Microdiffraction at Extreme Pressures and Temperatures

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary interiors, design materials with novel properties, understand the mechanical behavior of materials exposed to very high stresses as in explosions or impacts. Synthesis and structural analysis of materials at extreme conditions of pressure and temperature entails remarkable technical challenges. In the laser heated diamond anvil cell (LH-DAC), very high pressure is generated between the tips of two opposing diamond anvils forced against each other; focused infrared laser beams, shined through the diamonds, allow to reach very high temperatures on samples absorbing the laser radiation. When the LH-DAC is installed in a synchrotron beamline that provides extremely brilliant x-ray radiation, the structure of materials under extreme conditions can be probed in situ. LH-DAC samples, although very small, can show highly variable grain size, phase and chemical composition. In order to obtain the high resolution structural analysis and the most comprehensive characterization of a sample, we collect diffraction data in 2D grids and combine powder, single crystal and multigrain diffraction techniques. Representative results obtained in the synthesis of a new iron oxide, Fe4O5 1 will be shown.

The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary ...

Picoinjection of Microfluidic Drops Without Metal Electrodes

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of these electrodes adds cumbersome and error-prone steps to the device fabrication process. We have developed a technique that obviates the needs for metal electrodes during picoinjection. Instead, it uses the injection fluid itself as an electrode, since most biological reagents contain dissolved electrolytes and are conductive. By eliminating the electrodes, we reduce device fabrication time and complexity, and make the devices more robust. In addition, with our approach, the injection volume depends on the voltage applied to the picoinjection solution; this allows us to rapidly adjust the volume injected by modulating the applied voltage. We demonstrate that our technique is compatible with reagents incorporating common biological compounds, including buffers, enzymes, and nucleic acids.

We have developed a technique for picoinjecting microfluidic drops that does not require metal electrodes. As such, devices incorporating our technique are simpler to fabricate and to use.

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of ...

Synthesis of Zeolites Using the ADOR (Assembly-Disassembly-Organization-Reassembly) Route

Zeolites are an important class of materials that have wide ranging applications such as heterogeneous catalysts and adsorbents which are dependent on their framework topology. For new applications or improvements to existing ones, new zeolites with novel pore systems are desirable. We demonstrate a method for the synthesis of novel zeolites using the ADOR route. ADOR is an acronym for Assembly, Disassembly, Organization and Reassembly. This synthetic route takes advantage of the assembly of a relatively poorly stable that which can be selectively disassembled into a layered material. The resulting layered intermediate can then be organized in different manners by careful chemical manipulation and then reassembled into zeolites with new topologies. By carefully controlling the organization step of the synthetic pathway, new zeolites with never before seen topologies are capable of being synthesized. The structures of these new zeolites are confirmed using powder X-ray diffraction and further characterized by nitrogen adsorption and scanning electron microscopy. This new synthetic pathway for zeolites demonstrates its capability to produce novel frameworks that have never been prepared by traditional zeolite synthesis techniques.

Synthesis of Zeolites Using the ADOR Assembly-Disassembly-Organization-Reassembly Route

A protocol for the preparation of novel zeolites by the ADOR (Assembly-Disassembly-Organization-Reassembly) synthetic route is presented.

Zeolites are an important class of materials that have wide ranging applications such as heterogeneous catalysts and adsorbents which are dependent on ...

Chemistry

Operation of a 25 KWth Calcium Looping Pilot-plant with High Oxygen Concentrations in the Calciner

Calcium looping (CaL) is a post-combustion CO2 capture technology that is suitable for retrofitting existing power plants. The CaL process uses limestone as a cheap and readily available CO2 sorbent. While the technology has been widely studied, there are a few available options that could be applied to make it more economically viable. One of these is to increase the oxygen concentration in the calciner to reduce or eliminate the amount of recycled gas (CO2, H2O and impurities); therefore, decreasing or removing the energy necessary to heat the recycled gas stream. Moreover, there is a resulting increase in the energy input due to the change in the combustion intensity; this energy is used to enable the endothermic calcination reaction to occur in the absence of recycled flue gases. This paper presents the operation and first results of a CaL pilot plant with 100% oxygen combustion of natural gas in the calciner. The gas coming into the carbonator was a simulated flue gas from a coal-fired power plant or cement industry. Several limestone particle size distributions are also tested to further explore the effect of this parameter on the overall performance of this operating mode. The configuration of the reactor system, the operating procedures, and the results are described in detail in this paper. The reactor showed good hydrodynamic stability and stable CO2 capture, with capture efficiencies of up to 70% with a gas mixture simulating the flue gas of a coal-fired power plant.

Operation of a 25 KWth Calcium Looping Pilot-plant with High Oxygen Concentrations in the Calciner

This manuscript describes a procedure for operating a calcium looping pilot-plant for post-combustion carbon capture with high oxygen concentrations in the calciner in order to reduce or eliminate the flue gas recycle.

Calcium looping (CaL) is a post-combustion CO2 capture technology that is suitable for retrofitting existing power plants. The CaL process uses limestone ...

Environment

Blast Quantification Using Hopkinson Pressure Bars

Near-field blast load measurement presents an issue to many sensor types as they must endure very aggressive environments and be able to measure pressures up to many hundreds of megapascals. In this respect the simplicity of the Hopkinson pressure bar has a major advantage in that while the measurement end of the Hopkinson bar can endure and be exposed to harsh conditions, the strain gauge mounted to the bar can be affixed some distance away. This allows protective housings to be utilized which protect the strain gauge but do not interfere with the measurement acquisition. The use of an array of pressure bars allows the pressure-time histories at discrete known points to be measured. This article also describes the interpolation routine used to derive pressure-time histories at un-instrumented locations on the plane of interest. Currently the technique has been used to measure loading from high explosives in free air and buried shallowly in various soils.

This protocol details the use of Hopkinson pressure bars to measure reflected blast loading from near-field explosive events. It is capable of interpolating a pressure-time history at any point on a reflective boundary and as such can be used to fully characterize the spatial and temporal variations in loading produced.

Near-field blast load measurement presents an issue to many sensor types as they must endure very aggressive environments and be able to measure pressures ...

Adsorption Device Based on a Langatate Crystal Microbalance for High Temperature High Pressure Gas Adsorption in Zeolite H-ZSM-5

We present a high-temperature and high-pressure gas adsorption measurement device based on a high-frequency oscillating microbalance (5 MHz langatate crystal microbalance, LCM) and its use for gas adsorption measurements in zeolite H-ZSM-5. Prior to the adsorption measurements, zeolite H-ZSM-5 crystals were synthesized on the gold electrode in the center of the LCM, without covering the connection points of the gold electrodes to the oscillator, by the steam-assisted crystallization (SAC) method, so that the zeolite crystals remain attached to the oscillating microbalance while keeping good electroconductivity of the LCM during the adsorption measurements. Compared to a conventional quartz crystal microbalance (QCM) which is limited to temperatures below 80 &#176;C, the LCM can realize the adsorption measurements in principle at temperatures as high as 200-300 &#176;C (i.e., at or close to the reaction temperature of the target application of one-stage DME synthesis from the synthesis gas), owing to the absence of crystalline-phase transitions up to its melting point (1,470 &#176;C). The system was applied to investigate the adsorption of CO2, H2O, methanol and dimethyl ether (DME), each in the gas phase, on zeolite H-ZSM-5 in the temperature and pressure range of 50-150 &#176;C and 0-18 bar, respectively. The results showed that the adsorption isotherms of these gases in H-ZSM-5 can be well fitted by Langmuir-type adsorption isotherms. Furthermore, the determined adsorption parameters, i.e., adsorption capacities, adsorption enthalpies, and adsorption entropies, compare well to literature data. In this work, the results for CO2 are shown as an example.

A protocol for high-temperature and high-pressure gas adsorption measurements on zeolite H-ZSM-5 using an adsorption measurement device based on a langatate crystal microbalance is presented. Prior to the adsorption measurements, the synthesis of zeolite H-ZSM-5 on the langatate crystal microbalance sensor by the steam-assisted crystallization (SAC) method is demonstrated.

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Preparation of Biomass-based Mesoporous Carbon with Higher Nitrogen-/Oxygen-chelating Adsorption for Cu(II) Through Microwave Pre-Pyrolysis

An environment-friendly technique for synthesizing biomass-based mesoporous activated carbon with high nitrogen-/oxygen-chelating adsorption for Cu(II) is proposed. Bagasse impregnated with phosphoric acid is utilized as the precursor. To pyrolyze the precursor, two separate heating modes are used: microwave pyrolysis and conventional electric-heating pyrolysis. The resulting bagasse-derived carbon samples are modified with nitrification and reduction modification. Nitrogen (N)/oxygen (O) functional groups are simultaneously introduced to the surface of activated carbon, enhancing its adsorption of Cu(II) by complexing and ion-exchange. Characterization and copper adsorption experiments are performed to investigate the physicochemical properties of four prepared carbon samples and determine which heating method favors the subsequent modification for doping of N/O functional groups. In this technique, based on analyzing data of nitrogen adsorption, Fourier transform infrared spectroscopy, and batch adsorption experiments, it is proven that microwave-pyrolyzed carbon has more defect sites and, therefore, time-saving effective microwave pyrolysis contributes more N/O species to the carbon, although it leads to a lower specific surface area. This technique offers a promising route to synthesis adsorbents with higher nitrogen and oxygen content and a higher adsorption capacity of heavy-metal ions in wastewater remediation applications.

Preparation of Biomass-based Mesoporous Carbon with Higher Nitrogen-/Oxygen-chelating Adsorption for CuII Through Microwave Pre-Pyrolysis

Here, we present a protocol to synthesize nitrogen/oxygen dual-doped mesoporous carbon from biomass by chemical activation in different pyrolysis modes followed by modification. We demonstrate that the microwave pyrolysis benefits the subsequent modification process to simultaneously introduce more nitrogen and oxygen functional groups on the carbon.

An environment-friendly technique for synthesizing biomass-based mesoporous activated carbon with high nitrogen-/oxygen-chelating adsorption for Cu(II) is ...

Resource Recycling of Red Soil to Synthesize Fe2O3/FAU-type Zeolite Composite Material for Heavy Metal Removal

Heavy metal-polluted water is of great concern to human health and the eco-environment. In situ water remediation techniques enabled by highly efficient adsorption materials are of great importance in these circumstances. Among all the materials used in water remediation, iron-based nanomaterials and porous materials are of great interest, benefiting from their rich redox reactivity and adsorption function. Here, we developed a facile protocol to directly convert the widely spread red soil in south China to fabricate the Fe2O3/faujasite (FAU)-type zeolite composite material. 
The detailed synthesis procedure and synthesis parameters, such as reaction temperature, reaction time, and the Si/Al ratio in the raw materials, have been carefully tuned. The as-synthesized composite materials show good adsorption capacity for typical heavy metal(loid) ions. With 0.001 g/mL Fe2O3/FAU-type zeolite composite material added to different heavy metal(loid)-polluted aqueous solutions (single type of heavy metal(loid) concentration: 1,000 mg/L [ppm]), the adsorption capacity was shown to be 172, 45, 170, 40, 429, 693, 94, and 133 mg/g for Cu (II), Cr (III), Cr (VI), As (III), Cd (II), Pb (II), Zn (II), and Ni (II) removal, respectively, which can be further expanded for heavy metal-polluted water and soil remediation.

Resource Recycling of Red Soil to Synthesize Fe2O3/FAU-type Zeolite Composite Material for Heavy Metal Removal

This article presents a novel and convenient route to synthesize Fe2O3/faujasite (FAU)-type zeolite composite material from red soil. The detailed synthesis parameters have been finely tuned. The obtained composite material can be used for efficient heavy metal-contaminated water remediation, indicating its potential applications in environmental engineering.

Heavy metal-polluted water is of great concern to human health and the eco-environment. In situ water remediation techniques enabled by highly efficient ...

Impregnation and Grafting of Aminated Compounds onto Silica Substrates

A Synthetic Methodology for Preparing Impregnated and Grafted Amine-Based Silica Composites for Carbon Capture

Recently, there has been a significant effort towards reducing or mitigating CO2 emissions through the use of carbon capture materials for point source or direct air capture (DAC) methods. This work focuses on amine-functionalized CO2 adsorbents for DAC. These materials show promise for CO2 removal because they have low regeneration energy consumption and high adsorption capacity. The incorporation of amine species into a porous substrate combines the advantages of the amine species&#39; affinity to CO2 with the large pore volumes and surface areas of the porous substrate. There are three methods commonly used to prepare amine-based CO2 sorbents, depending on the selection of the amine species, material support, and preparation method. These methods are impregnation, grafting, or chemical synthesis. Silica is a prevalent choice of substrate material because of its adjustable pore size, moisture tolerance, temperature stability, and ability to adsorb CO2 in low concentrations for DAC applications. Typical synthetic procedures and primary attributes of both impregnated and grafted amine-silica composites are described herein.

Author Spotlight: Standardizing the Development of Amine-Based Silica Composites as CO2 Adsorbents for Direct Air Capture 

This work aims to facilitate the development of standardized techniques for impregnating or grafting aminated compounds onto silica substrates, which are often broadly described in the literature. Specific amounts of solvent, substrate, amines, and the values of other important experimental parameters will be discussed in detail.

Recently, there has been a significant effort towards reducing or mitigating CO2 emissions through the use of carbon capture materials for point source or ...

Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

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