Adsorption of heavy metals from acid mine drainage by natural zeolite

The adsorption behaviour of natural zeolite (clinoptilolite) has been studied in order to determine its applicability in treating acid mine drainage (AMD) containing 400, 20, 20 and 120 mgl − 1 of Fe 3+, Cu 2+, Mn 2+ and Zn 2+ respectively. Tests to determine both the rate of adsorption and the uptake at equilibrium were performed under batch conditions from single and multi-component solutions. The optimum conditions for the treatment process were investigated by observing the influence of pH levels, the presence of competing ions, varying the mass of zeolite and thermal modification of the natural zeolite (calcination and microwaves). The adsorption studies showed rapid uptake in general for the first 40 mins, corresponding to ∼ 80% total removal. After this initial rapid period, the rate of adsorption decreases. According to the equilibrium studies, the selectivity sequence can be given as Fe 3+ > Zn 2+ > Cu 2+ > Mn 2+, with good fits being obtained using Langmuir and Freundlich adsorption isotherms. Preliminary tests using AMD samples from Wheal Jane Mine, UK, showed that natural zeolite has great potential as an alternative low cost material in the treatment of acid mine drainage.