Utilizing metakaolin and siliceous waste from the alum industry to create geopolymer adsorbent for the removal of certain heavy metals.

A geopolymer (GP) from Partially Dealuminated Kaolin (PDK) was synthesized. PDK is a solid waste of alum industry, it was produced in a big quantity, which need careful management to be recycled for protection of the environment against pollution. Utilization of PDK is very lacking, and there were no studies for using in the preparation of geopolymer as an adsorbent for heavy metal removal from wastewater. GP was used for the removal of Cr, Cd, and Pb from synthetic industrial wastewater by the adsorption technique. FTIR spectrum indicates a peak at 977 cm due to Si-O-Si and Si-O-Al bonds confirming the formation of geopolymer. The effects of various parameters such as temperature, pH, contact time, and metal ion concentration were tested to stand over the most favorable conditions for adsorption. A total of 100% removal was achieved at a pH = 6.0, temperature = 25 °C, and initial concentration = 40 mg/L for a contact time of 60 min using a dosage of 0.2 g/L. The adsorption data validated Freundlich adsorption model. The values of Freundlich constant value, R were greater than 0.99 indicating the adsorption of metal ions onto the geopolymer to be highly favorable. High adsorption capacity has been achieved for Pb, Cd, and Cr (105.6 mg/g for Pb, 150 mg/g for Cd, 125 mg/g for Cr). The adsorption process followed pseudo-1st-order kinetics yielding high correlation coefficient and the adsorbed amount at equilibrium. More than 95% of adsorption was achieved at room temperature supports the effectiveness of metal ions adsorption on the geopolymer. This work helps for the reuse of the industrial waste of alum industry through the synthesis of a geopolymeric adsorbent, which can be applied successfully for removal of the Pb, Cd, and Cr ions from the polluted water.