The present study aims at the synthesis of highly efficient, three dimensional, porous, alumino-silicate geopolymeric adsorbents derived from the steel plant LD (Linz-Donawitz) slag, a potential raw material for geopolymerisation, to remove toxic fluoride ions from wastewater. LD slag geopolymeric adsorbent (LDSGP) has been chemically modified by bivalent metallic ions i.e. Ni2+ and Zn2+ separately resulting formation of Ni-LDSGP & Zn-LDSGP adsorbents respectively; and their fluoride adsorption capacities have been investigated. The physico-chemical properties of all the geopolymeric adsorbents have been described by using standard characterization techniques including BET, FESEM & HRTEM, FTIR, XRD etc. showing micro-petal like morphology on its' outer surfaces. The fluoride sorption onto the geopolymeric adsorbents have been investigated in batch adsorption studies where Zn-LDSGP adsorbent has the superior fluoride adsorption capacity followed by Ni-LDSGP and LDSGP (Q(e,Zn-LDSGP) = 60 mg/g> Q(e,Ni-LDSGP) = 55.4 mg/g> Q(e,LDSGP) = 50.6 mg/g). The equilibrium study shows best fit to Freundlich model while the adsorption kinetic data fitted best with pseudo-second-order model suggesting the nature of the adsorption to be chemisorption. The mass transfer occurred during the sorption process has been mathematically modeled and simulated to identify the rate-determining steps of mass transfer phenomena. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.