Motsi, Tafadzwa
(2010).
Remediation of acid mine drainage using natural zeolite.
University of Birmingham.
Ph.D.
Abstract
This research focuses on the removal of Fe, Cu, Zn and Mn from synthetic metal solutions and real AMD from Wheal Jane mine using natural zeolite. Laboratory experiments were performed to investigate the effectiveness of natural zeolite as a potential low cost material for the removal of these heavy metals from AMD. These include, equilibrium tests, batch kinetic studies, column studies and desorption studies.
Equilibrium studies showed that the capacity of natural zeolite for heavy metals increased with an increase in initial solution pH. Fitting of the Langmuir and Freundlich isotherms to experimental data gave good fits, R\(^2\) values ranging from 0.9 – 0.99. The selectivity series of natural zeolite was: Fe\(^{3+}\)>Zn\(^{2+}\)>Cu\(^{2+}\)>Mn\(^{2+}\). The amount of exchangeable cations increased at equilibrium, indicating that ion exchange had taken place. Higher metal uptakes were achieved by increasing agitation speed, initial solution pH, particle size reduction, and thermal pre-treatment. The rate limiting step for this process was intraparticle diffusion.
Column studies showed that natural zeolite was capable of removing heavy metals from a continuously flowing solution. The breakthrough time increased with a longer bed height and slower flow rate. The bed depth service time model (BDST) was used to simulate experimental data and deviated from these by 12 – 14%.
The treatment of actual Wheal Jane mine AMD showed that about 71-99% Fe and 97-99% Cu were removed from solution. Results from the treatment of actual AMD revealed that natural zeolite was best suited for treating dilute metal solutions, and hence should be used downstream of other AMD treatment technologies.
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