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

The overall goal of this procedure is to synthesize precipitated calcium carbonate of high purity in zeolitic material of satisfactory heavy metal absorption capacity from iron-making blast furnace slag while managing to store significant amounts of CO2 and eliminating potential residues. This method helps address a key issue related to the conversion of metallurgical slags into carbon sinks through indirect carbonation. Namely, the valorization of the solid residue resulting from the calcium extraction process.

The main advantage of this technique is its integrated nature that leads to the parallel production of two value added material while leaving no waste behind. Demonstrating the procedure will be Jaspreet Chandla, a technologist at the Sheridan Chemical and Environmental Laboratoryies as well as Hiba Batool, a graduate of our environmental control program. To begin this procedure, use a mortar and pestle to grind blast furnace slag.

Sift to a particle size less than two millimeters. Next, unseal a properly equipped autoclave reactor. Place 100 grams of the sieved slag into the vessel.

Add 731 milliliters of two molar acetic acid. The seal the autoclave reactor. Place the heating jacket such that it covers the vessel.

Set the heating temperature to 30 degrees Celsius and the mixing speed to 1, 000 RPM. Once the interior temperature reaches the set point, leave the slurry to mix for 60 minutes. After the acid extraction time has elapsed, remove the heating jacket.

Then unseal the reactor. And pour the slurry into a beaker. Using vacuum filtration, separate the leachated solution from the residual solids.

Next clean both the reactor head and the vessel with de-ionized water. Place the filtered residual solids into the vessel and add 731 milliliters of two molar acetic acid. Seal the reactor.

Then mount the reactor with the thermocouple and heating jacket. Then set the heating temperature to 30 degrees Celsius and the mixing speed to 1, 000 RPM. Once the vessel’s interior temperature has reached the set point, mix the slurry for 60 minutes.

Pour the resulting slurry into centrifuge tubes. Centrifuge at 2, 500 times G for 10 minutes. After centrifugation is complete, slowly pour the supernatants into a bottle.

Combine the solutions from each extraction to obtain the post-extraction leachate. Then add concentrated sodium hydroxide solution and purify the leachate as outlined in the text protocol. Calcium extraction is critical to the overall process.

The extraction extent achieved and the leaching selectivity obtained with determine the purity level of the precipitated calcium carbonate and the composition of the zeolitic material. To begin, pour the purified leachate into a clean autoclave reactor. Add a 50 percent sodium hydroxide solution to the vessel such that the final concentration of sodium hydroxide is 1.7 molar.

After this, seal the reactor and place the heating jacket. Set the heating temperature to 30 degrees Celsius and the mixing speed to 1, 000 RPM. Once the desire interior temperature is reached introduce high purity CO2 at two bar for 60 minutes.

Then remove the heating jacket and unseal the reactor. Pour the carbonated slurry into a beaker. Vacuum filter the slurry, separating the solid precipitates from the solution.

Rinse the filter cake thoroughly with de-ionized water under vacuum to remove any soluble sodium. After this, oven dry the solid material at 105 degrees Celsius for 24 hours to retrieve the precipitated calcium carbonate. Place 60 grams of dry residual solids, centrifuged and rinsed during calcium extraction into a clean autoclave reactor.

Add 300 milliliters of two molar sodium hydroxide solution. Then seal the reactor. And fasten it to its support.

Place the heating jacket and set the temperature to 150 degrees Celsius. After this, begin mixing the slurry at 300 RPM. Once the interior of the reactor reaches the desired temperature, leave the slurry to mix for 24 hours.

After mixing is complete, remove the heating jacket and allow the reactor to cool for one hour. Then unseal the reactor and pour the slurry into a beaker. Using vacuum filtration, separate the converted solids from the solution.

Rinse the solids thoroughly with de-ionized water under vacuum. Next, oven dry the filtered material for 24 hours at 105 degrees Celsius to obtain the hydrothermally converted material. Using a mortar and pestle, desegregate the granular material.

After this, sieve the resulting material to a particle size smaller than 85 milliters. To begin, transfer 100 milliliters of each synthetically prepared contaminated solution into a separate capped plastic bottle. Then disperse one gram of the hydrothermally converted material into each bottle.

Add concentrated sodium hydroxide, dropwise to each solution, adjusting the Ph until it is between four and five. After this, place the bottles in a shaker incubator. Agitate at 160 RPM and 20 degrees Celsius for 24 hours.

The next day, add concentrated hydrochloric acid to readjust the Ph until it is between four and five. Then pour the slurry into a centrifuge tube. Centrifuge at 2500 times G for five minutes.

The concentrations of acids and bases used for the Ph adjustment steps should be reduced as the target Ph approaches, since it is not far from neutral. And the additions must be done patiently dropwise and with continuous stirring. Next, carefully pour each supernatant into a new bottle.

Keeping the solids in the centrifuge tube. Add a two percent nitric acid solution until the Ph is below two. Then, analyze the heavy metal in the supernatant as outline in the text protocol.

In this study, calcium is selectively extracted from blast furnace slag through leaching with acetic acid. Inductively coupled plasma mass spectrometry analysis reveals that after two rounds of leaching, approximately 90 percent of the calcium has been extracted. Silica and aluminum are seen to remain in the solid phase.

Which is necessary for the production of alumino-silicate based zeolitic materials through hydrothermal conversion. The purified leachate solution then undergoes carbonation, producing precipitated calcium carbonate. X-ray defraction reveals that calcite is the mineral phase that was primarily synthesized.

And the mean particle size is seen to be small with a narrow particle size distribution. In parallel with carbonation, the solid residues from the extraction stage are subjected to hydrothermal conversion. X-ray defraction reveals the presence of two main phases in recovered material.

Analcime and tobermorite. Absorption isotherm data, both experimental and simulated of nickel two plus on the zeolitic material is then compared. These comparisons show that the Langmuir equation closely fits the experimental data.

This suggests a monolayer absorption of nickel plus two ions on the converted material via a cami-absorption process. The Tempkin model is also seen to fit the experimental data well. The positive variation of absorption energy reveals that the absorption is exothermic.

After watching this video we should have a good understanding of how to synthesize high purity precipitated calcium carbonate in zeolitic material with heavy metal absorption capacity through the indirect carbonation of blast furnace slag and the hydrothermal conversion of the residual solids from the extraction step. While attempting this procedure it’s important to remember that the composition and characteristics of slags and other calcium rich industrial residues may differ substantially from that of the blast furnace slag herein used. So procedural adjustments may be required to obtain similar product properties.

Following this procedure, testing of the zeolitic materials for other waste water or remediation applications can be performed as they likely have absorption capacity for other heavy metals such as cadmium, lead and zinc. Don’t forget that working with concentrated acids and bases and with pressurized and high temperature reactor can be extremely hazardous. So precautions such as wearing safety gloves and glasses and strict adherence to the protocols should always be taken while performing the procedure.