Using tailings as heavy metal adsorbents — The effect of buffering capacity

Previous studies have shown that silicate tailings could be used to treat heavy metal polluted water and to stabilise heavy metals in waste deposits and contaminated sediments. Adsorption to particle surfaces and hydroxide precipitation are thought to be the principal immobilisation mechanisms. To achieve optimal adsorption it is often necessary to increase the pH of the system. When using adsorbents possessing a capacity to neutralise acid, the pH increase could be achieved automatically and without any addition of chemicals. In this study the copper adsorption characteristics and buffering capacities of dust from the crushing and milling of nepheline syenite were investigated. The results were compared with the performance of a glacimarine clay, and showed that the nepheline syenite dust had superior buffer capacities and a superior ability to adsorb copper when exposed to initially acidic solutions. The results also indicated that chemisorption takes place on the nepheline syenite material, while adsorption on the clay is of a physical nature.