Development of sustainable adsorbents for wastewater treatment

• Main Author: Manchisi, James
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2016

The purpose of this study was to develop adsorbents from slag materials as a low cost method to purify acid mine drainage of high acidity and toxic metal ions content. The study included adsorbent characterisation and adsorption experiments to understand the adsorption behaviour of a multi-adsorbate system of Cd\(2\)\(+\), Co\(2\)\(+\), Cu\(2\)\(+\), Fe\(2\)\(+\) and Mn\(2\)\(+\) ions. It was found that the adsorbents had low surface area and unfavourable pore size distribution. The chemical activation of the adsorbents improved the adsorbent properties, and thus increased amounts of metal ions adsorbed. However, the adsorption of multiple metal ions was only effective in dilute solutions, with adsorption efficiency increasing with increase in phase ratio, pH and temperature. The adsorption data was best described by pseudo second order kinetic and double exponential diffusion models. The mechanisms involved adsorption, precipitation and ion exchange. The adsorbent capacities were relatively low, with selectivity proposed as Fe\(2\)\(+\)>Cu\(2\)\(+\)> Cd\(2\)\(+\)>Co\(2\)\(+\)>Mn\(2\)\(+\). The fixed bed efficiencies were satisfactory but the adsorbents were easily exhausted, which indicated a limited ability for the adsorbent materials to be regenerated. However, desorption of metal ions was favourable, and this may provide an opportunity for metal ions to be recovered and for spent adsorbents to be disposed safely.