Metakaolin based geopolymer as an effective adsorbent for adsorption of zinc(II) and nickel(II) ions from aqueous solutions

Metakaolin based geopolymer (MKG) was investigated as an adsorbent to remove Zn(II) and Ni(II) ions from aqueous solution. The parameters of initial pH, adsorbent amount, time of contact and initial metal ion concentration on the metal removal performance of MKG were studied using a batch method at 25 °C. The amount of Zn(II) and Ni(II) ions adsorbed onto MKG increased with increasing contact time with an adsorption equilibrium being reached within 40 min and 50 min for Zn(II) and Ni(II), respectively. The optimum values of initial pH were 6.39 for Zn(II) and 7.25 for Ni(II). The uptake of Zn(II) and Ni(II) ions by MKG was observed to decrease by increasing the adsorbent amount. The Langmuir isotherm described the adsorption data very well and the maximum monolayer adsorption capacities determined from the Langmuir adsorption isotherm were found to be 1.14 × 10− 3 and 7.26 × 10− 4 mol g− 1 for Zn(II) and Ni(II), respectively. The kinetic studies showed that adsorption followed the pseudo-second-order kinetic model. The continuous mode adsorption studies showed the optimum flow rates were 2.0 mL min− 1 for Zn(II) and 1.0 mL min− 1 for Ni(II). The breakthrough points were observed at 150 and 280 min for Zn(II) and Ni(II), respectively. It is concluded that Zn(II) and Ni(II) ions in aqueous solutions are efficiently removed by MKG which could be employed as a low-cost and excellent alternative for wastewater treatment.