The provided information describes how to make silica gel, but not specifically how to make "silica gel sand" in the granular form typically sold as a desiccant or pet litter. The process below outlines how silica gel can be created from grain husk ash and then describes how to obtain a granular form akin to "silica gel sand."
Steps to Produce Silica Gel from Grain Husk Ash:
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Burn Grain Husk to Ash: Start by burning grain husk (e.g., rice husk) to produce burned ash. This ash is rich in silica.
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Prepare Alkaline Solution: Prepare a strongly alkaline aqueous solution containing an alkali metal compound (e.g., sodium hydroxide (NaOH) or potassium hydroxide (KOH)). The concentration of the solution is important for the subsequent extraction process.
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Mix Ash with Alkaline Solution: Charge the burned ash into the alkaline solution.
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Agitate the Mixture: Thoroughly agitate or stir the mixture to ensure the silica in the ash reacts with the alkaline solution. This process extracts the silica, forming sodium silicate or potassium silicate, often referred to as "water glass."
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Heat the Mixture: Heat the mixture to promote the dissolution of silica from the ash into the alkaline solution. The temperature needs to be controlled to optimize the extraction.
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Separate the Mixture: Separate the liquid from any undissolved solids. This can be done by filtration, decantation, or centrifugation. The liquid contains the dissolved silica.
Transforming the Silica Gel into "Silica Gel Sand" Granules:
The above process yields a solution containing silica. To create silica gel "sand" (granules):
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Gelation: The extracted silica solution (e.g., sodium silicate) must be gelled. This is typically done by carefully neutralizing the alkaline solution with an acid (e.g., sulfuric acid, hydrochloric acid). The pH needs to be carefully controlled to achieve optimal gel formation. As the pH decreases, the silicate molecules polymerize and form a gel network.
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Washing: The gel needs to be thoroughly washed to remove the alkali metal salts (e.g., sodium sulfate if sulfuric acid was used). This is crucial for the final product's purity and adsorption properties. Repeated washing with deionized water is common.
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Drying: The washed gel is then dried to remove water. This is typically done using a drying oven or spray dryer. The drying temperature and time will influence the pore size and surface area of the final silica gel.
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Crushing and Sieving: The dried silica gel is often in a large, irregular mass. To create granules resembling "sand," it needs to be crushed and then sieved to obtain the desired particle size range. Different mesh sizes can be used to separate the crushed silica gel into various size fractions.
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Activation (Optional): To improve the adsorption capacity of the silica gel "sand", it can be activated by heating it to a high temperature (e.g., 120-200°C) to remove any remaining moisture and volatile organic compounds.
Therefore, "silica gel sand" is not directly "made," but rather silica gel is synthesized and then processed (crushed and sieved) into a granular form.
