Optimisation of semi-upscaled polymer inclusion membrane (PIMs) based device for passive remediation of metal ions in acid mine drainage (AMD)

Acid mine drainage (AMD) has been a source of environmental contamination in many parts of the world. This is because many countries depend on mining as a source of revenue. However, waste tailing dumps often leach out toxic waste with high levels of metal ions and flow downstream to dams and rivers. The current remediation methods (passive and active) are expensive or ineffective for long-term use. In some cases, these methods generate solid slag waste as a major by-product. However, as part of the green and circular economy, waste materials are viewed as potential resources for raw materials. This work then reports on the design, laboratory optimisation and early-stage application of semi-pilot passive remediation device for the possible recovery of metal ions (cadmium, cobalt, copper, iron, and nickel) in AMD generated in the tailings pond. The sampling remediation device consisted of a polymer inclusion membrane composed of polyvinyl chloride and di-(2-eth-ylhexyl) phosphoric acid as a semi-penetrable barrier. The device had an upscaled chamber made of nylon with 1000 mL of the receiving solution. This developed passive remediation device was used in both synthetic and real AMD samples where a linear uptake of metals was demonstrated from day 6 to over a month with little influence of matrices. During deployment, the pH was increasing in the receiving solution and decreasing in the source solution of the linear region thus indicating the analytes facilitated transport. On day 35 of environmental application accumulated concentrations of target metal ions were Ni (63.42 mg L-1), Cd (47.48 mg L-1), Co (57.34 mg L-1), and Cu (49.86 mg L-1). Further, the characterisation results showed no signs of membrane degradation in this period. This highlights that the PIMs are a promising future for passive remediation and/or recovery of metal ions in mine wastewater before contamination of rivers and dams downstream.

Automated summary

Acid mine drainage (AMD) is a significant source of environmental contamination, and current remediation methods are expensive or ineffective. This study reports on the design and application of a passive remediation device using a polymer inclusion membrane to recover metal ions from AMD. The results show promising potential for this method in the future.