Evaluation of nanofiltration membranes for recovery and concentration of rare earth elements from acidic waters

Abstract

Acid Mine Drainage (AMD) is a by-product of mining industry which represents an environmental problem in terms of its acidity and high content of heavy metals. These properties make aqueous streams to be a toxic mixture that will damage aquatic life, destroys ecosystems and taints water. Different techniques are applied to solve this problem where metal ions precipitation and acidic neutralization by lime addition are the best options in terms of cost and benefit. Nanofiltration membranes present good performance to separate metal ions from aqueous solutions, so given this property; a commercial available aromatic polyamide membrane (NF-270) was tested to treat simulated acidic water. Experiments were carried out with different membrane samples in a flat-sheet module. Two of the membranes tested were immersed in sulphuric acid 0,1 and 1 M for one month. Feed solution contains a high content in aluminium and sulphate and it has in lesser concentration transition metals (Ca, Cu, Zn) and rare earth elements (La, Pr, Nd, Sm, Dy, Yb). Virgin NF-270 membrane presents metal rejection higher than 98 % and the membrane immersed in 0.1 M H2SO4 exhibits same behaviour. The membrane aged in 1 M H2SO4 presented metal rejection around 70 %, which suggest membrane properties were modified due to strong acidic conditions. A new challenge is to study the physic-chemical changes occurred on the polyamide membrane.