Removal of metal ions from an acidic leachate solution by nanofiltration membranes

This paper presents the feasibility of the application of two commercial nanofiltration (NF) membranes (Desal5 DK and NF-270) in the removal of metal ions from an acidic leachate solution generated from a contaminated soil using H2SO4 as a soil washing agent. The experimental results of soil washing indicated that H2SO4 is highly effective in removing metal ions from contaminated soil. Following this process, the treatment of this acidic solution by nanofiltration membranes showed good metal ion rejection (between 62% to 100%) where divalent ions were better rejected than monovalent ions. For characterization purposes, the membrane experiments were conducted using K2SO4 solutions at different pHs. Membrane performance criteria were evaluated according to membrane permeability and ionic retention in the tank and permeate, taking into account different operating conditions such as pressures, flow rate and pH. These results demonstrated the effectiveness and feasibility of the application of nanofiltration treatments in the cleaning-up of contaminated water residues generated during soil washing processes.

The removal of pollutants from soils is one of the most challenging environmental tasks. For that reason, this study was intended to evaluate two NF membranes for the recovery of ions coming from contaminated soil. The experimental results have successfully demonstrated that the use of the washing solution H2SO4 has a high extraction efficiency in the removal of ions from contaminated soils. During the application of NF membranes in the treatment of the acidic leachate solution, the commercial membrane showed high ion selectivity. Additionally it demonstrated a good removal of TOC during the filtration experiment (70–89%). During the filtration experiments, the Desal5 DK membrane demonstrated an increase in dynamic permeability, showing its dependence to the electrolyte solutions. On the other hand, the NF-270 membrane presented an opposite behaviour: a decrease in dynamic permeability. These results indicate that the best candidate for the removal of metal ions was Desal5 DK, which presented good membrane permeability combined with good ion retention and acidic resistance. During this investigation it has been demonstrated that the application of NF processes will bring about the elimination of metal ions from waste waters, a possible recovery of acid during the process and a reduction of the amount of inorganic and organic waste.