(545p) Fluoride Removal By Geopolymeric Adsorbent Synthesized from LD Slag

This research aims at investigating the utilization of steel plant LD (Linz-Donawitz) slag as a potential raw material for synthesis of LD slag based geopolymer (LDSGP) adsorbent to remove toxic fluoride ions from artificial wastewater. Steel-making LD slag, a solid waste of steel industries, is generated when the molten steel is separated from impurities, in LD (Linz-Donawitz) furnaces. It consists of mainly calcium oxide and iron oxide along with silica etc. Raw LD slag has been mechanically mixed with an alkaline activator (10M NaOH + sodium silicate (1:1 w/w)) at weight ratio of 2:1 and then cured for 3 days at 25⁰ C to prepare LD slag based porous aluminosilicate geopolymeric adsorbent. The physical and chemical properties of new LD slag geopolymeric adsorbent has been characterized using BET, FTIR, XRD, SEM & TEM etc. which show an increase of BET surface area (from 4.85 to 30.84 m2/g) and formation of Ca₂SiO₄ and Ca₃SiO₅ in the aluminosilicate geopolymeric matrix. The micro-petal like morphology of LDSGP surface has been obtained. Batch adsorption experiments of fluoride ions onto LDSGP adsorbent has been carried out to investigate the effect of operating parameter i.e. different adsorbent dose, pH of the solution, initial fluoride concentration at different temperature. Isotherm study at equilibrium shows best fit to Freudlich model and the maximum experimental adsorption uptake has been achieved as 50.6 mg/g. Adsorption kinetic data fitted with pseudo-second-order model suggesting the nature of the adsorbent to be chemisorption. Thermodynamic study proves the spontaneous nature of the fluoride adsorption process onto LDSGP.