(359e) Preparation of Geopolymeric Adsorbent Derived from LD Slag for Removal of Zinc (II) from Waste Water

In this work, LD slag Geopolymer (LDSGP), a porous aluminosillicate geopolymeric adsorbent has been successfully prepared from steel plant LD slag for efficient removal of Zinc ions (Zn²⁺), one of the most toxic heavy metals present in waste water. LD slag, a high calcium oxide rich solid waste, is generated in huge quantity while producing high quality steel from pig iron using Linz Donawitz (LD) converters. Presently, disposal of LD slag has become a major environmental concern for the industries. So, geopolymerization of LD slag is attempted to reuse it as a low cost adsorbent in waste water treatment by removing Zn²⁺, thus presenting a solution for both treating a problematic wastewater and turning industrial waste into a valuable material. The geopolymerisation process is a series of chemical reactions that include alkali activation of raw LDS, polycondensation of aluminosillicate and structural re-organisation. LD slag geopolymer (LDSGP) was synthesized in a plastic mould where the colloid mixture of raw LD slag and alkaline activator (sodium hydroxide and sodium silicate (1:1 w/w)) were cured for 3 days at room temperature. The LDSGP was characterized by using XRF technique, BET surface area, SEM & TEM images, PXRD patterns, FTIR spectra and TGA. The BET surface area of LDSGP (30.84 m²/g) is improved considerably compared to raw LDS (4.85 m²/g). The PXRD pattern of LDSGP confirms the formation of tetrahedral geopolymer matrix consisting Ca₂SiO₄ and Ca₃SiO₅. The SEM and TEM images of the LDSGP particles reveal the combination of micropetal and cauliflower like structures on the surface. The equilibrium data from batch experiments for the adsorption study of Zn²⁺ ions at 298 K was successfully fitted with the Langmuir isotherm. The maximum adsorption uptake of Zn²⁺, onto LDSGP, was found to be 84.125 mg/g at 298 K. The adsorption rate data was better correlated to pseudo-second-order model indicating the process to be dominated by chemisorption.