Abstract
Acid mine drainage (AMD), an acidic effluent characterized by high concentrations of sulfate and heavy metals, is an environmental and economic concern. The performance of an integrated submerged direct contact membrane distillation (DCMD) – zeolite sorption system for AMD treatment was evaluated. The results showed that modified (heat treated) zeolite achieved 26–30% higher removal of heavy metals compared to natural untreated zeolite. Heavy metal sorption by heat treated zeolite followed the order of Fe > Al > Zn > Cu > Ni and the data fitted well to Langmuir and pseudo second order kinetics model. Slight pH adjustment from 2 to 4 significantly increased Fe and Al removal rate (close to 100%) due to a combination of sorption and partial precipitation. An integrated system of submerged DCMD with zeolite for AMD treatment enabled to achieve 50% water recovery in 30 h. The integrated system provided a favourable condition for zeolite to be used in powder form with full contact time. Likewise, heavy metal removal from AMD by zeolite, specifically Fe and Al, mitigated membrane fouling on the surface of the hollow fiber submerged membrane. The integrated system produced high quality fresh water while concentrating sulfuric acid and valuable heavy metals (Cu, Zn and Ni).
Highlights
The formation of acid mine drainage (AMD) is a natural process attributed to the oxidation of sulfide minerals such as pyrites (Kalin et al, 2006; Mosley et al, 2018)
This study evaluated the potential of combining submerged direct contact membrane distillation (DCMD) and zeolite into a single integrated process
The sorption capacity of natural and modified zeolite was tested for heavy metal removal from AMD
Summary
The formation of acid mine drainage (AMD) is a natural process attributed to the oxidation of sulfide minerals such as pyrites (Kalin et al, 2006; Mosley et al, 2018). Active and abandoned mines intensifies the formation of AMD due to open pits, mining waste rock, structures and tailings that are exposed to water, air and bacterial activity (Kalin et al, 2006; Mosley et al, 2018; Tolonen et al, 2014). AMD is characterized by low pH and high concentration of sulfate, as well as high concentrations of heavy metals activity (Kalin et al., 2006; Mosley et al, 2018; Tolonen et al, 2014). The long-term impact of AMD contaminant on aquatic organisms, plant growth and human health is a significant concern, which necessitates AMD treatment (Mosley et al., 2018)
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