Direct contact membrane distillation as an alternative to the conventional methods for value-added compounds recovery from acidic effluents: A review

The biggest challenge that the mining and metallurgic industry faces is overcoming the contradictions between this activity benefits and environmental costs. One of the steps that causes the greatest damage to the environment and human health refers to acid mine drainage (AMD) and pickling solutions, which is a result of certain sulfide minerals oxidation. This process causes water acidification as well as the considerable increase in metals and sulfate concentrations on aqueous matrices restricting its use. Thus, it is necessary to adopt cleaner production methods to meet increasingly restrictive environmental legislation and, moreover, allow the possibility to recover these sub-products, generating operational economic savings. In this scenario the membrane distillation (MD) application, which is based on the vapor pressure difference between the two sides of hydrophobic membrane surfaces, stands out. Among the MD process the direct contact membrane distillation (DCMD) is highlighted, it has several advantages, such as its ability of 100% (theoretical) macromolecules rejection, in addition to non-volatile compounds and inorganic ions. Moreover, MD operates at relatively low temperature and lower operating pressures when compared to the classical membrane separation processes (MSP), producing high-quality water. These MD characteristics prove that this method is able to treat the AMD and pickling solutions.