An investigation into precipitate behaviour for effective operation of settling tanks through selective precipitation

Abstract

Selective precipitation (SP) is a promising remediation technique for mine drainage, minimising generation of waste sludge. The efficiency of SP is heavily dependent on how effectively precipitates fall out in a settling tank. In this research, the behaviour of iron precipitate was examined using a one dimensional column, with mine drainage pumped upwards through the settling tank. The behaviour was determined by a balance of precipitate settling and floating velocities. The experimental parameters affecting the vertical velocity of precipitates included mine drainage vertical velocity, column height and flocculant addition. The upper sediment accelerated precipitate flocculation in the input mine drainage, reducing turbidity of mine drainage discharge – a self‐filtering effect. For effective operation, discharge turbidity must be minimised and the top upper sediment edge maintained near the upper outlet. This was achieved by continuously removing precipitate from the lower outlet of the settling tank at the rate it was generated.