The Adsorption of Heavy Metals from Aqueous Solutions Using Silica Microparticles Synthesized from Sodium Silicate

Abstract

Silica microparticles synthesized from sodium silicate were characterized and used as an adsorbent for lead and nickel ions (Pb2+ and Ni2+) from their separate solutions. Batch adsorption experimental results showed that an increase in the percentage removals of the Pb2+ and Ni2+ ions from their solutions was favoured by increased contact time, adsorbent dosage, and heavy metal ion concentrations. Optimum adsorptions of 59.40%/64.66%, 61.4%/75.60% and 61.4%/49.58% for Pb2+/Ni2+ ions were obtained at contact time of 40 min, an adsorbent dosage of 2.5 g and heavy metal ion concentration of 50/40 mg/l respectively. The adsorption data were subjected to different kinetic models and pseudo-second-order reaction model had the best fit for both metal ions (R2, 0.985, 0.996). To verify the adsorption performance, the adsorption data were also fitted into the Langmuir and Freundlich isotherms. The Langmuir isotherm had the best fit for both metal ions (R2, 0.918, 0.872). The maximum metal ion capacity calculated from Langmuir isotherm was 22.3 and 25.5 mg g−1 for lead and nickel ions, respectively. This study showed that silica microparticles can bind a substantial amount of lead and nickel ions from aqueous solutions.