Controlling calcium sulphate scale formation in acid mine waters

Abstract

Membrane technologies are capable of treating mine waste waters to produce clean permeate water for reuse and a concentrate stream that can be used for valuable metals recovery. Reverse Osmosis (RO), Nano-filtration (NF) and Ultra-filtration (UF) technology is increasingly being adopted. In precious metal mines, waste water can be concentrated using membrane plant so additional metals can be recovered from barren liquor. Acid mine drainage (AMD) is increasingly treated and then reused or sent off site as a valuable resource for domestic and agricultural use. The use of membrane technology is hampered by the potential for rapid membrane fouling and calcium sulphate (gypsum) scale deposition. The authors have embarked on research project to investigate calcium sulphate scale formation in acidic pH and in the presence of a variety of soluble metals. New antiscalant chemistry for preventing sulphate scale formation in acidic conditions with metals have been investigated and the results are presented. A series of experiments were performed to assess calcium sulphate scale formation and inhibition in the presence of metals at low pH. The dissociation of sulphate and bi-sulphate ions at low pH was investigated, followed by Threshold jar tests to screen water chemistries at different conditions and finally using actual membrane coupons with a Flat Sheet Test rig to assess membrane performance and scaling inhibition.