DESALINATION OF CALCIUM-SULFATE SCALING MINE WATER - DESIGN AND OPERATION OF THE SPARRO PROCESS

The South African mining industry discharges relatively small quantiti es of mine service water to the environment, but these effluents contr ibute substantially to the salt load of the receiving waters. The poor quality of service water also has significant cost implications on th e mining operations. Of the two main types of mine service water encou ntered in the gold mining industry, the so-called calcium sulphate sca ling types is found in the majority of cases. Preliminary testwork on this type of water using membrane desalination processes revealed that only the seeded reverse osmosis type of process showed promise. To ov ercome certain process problems and high operating costs with this sys tem, a novel membrane desalination technique incorporating seeded tech nology, called the SPARRO (slurry precipitation and recycle reverse os mosis) process, was developed. The novel features of the new process i ncluded; a lower linear slurry velocity in the membrane tubes, a lower seed slurry concentration, a dual pumping arrangement to a tapered me mbrane stack, a smaller reactor and a modified seed crystal and brine blow-down system. Evaluation of the SPARRO process and its novel featu res, over a five-year period, confirmed its technical viability for de salinating calcium sulphate-scaling mine water. The electrical power c onsumption of the process was approximately half that of previous desi gns, significantly improving its efficiency. Membrane performance was evaluated and was generally unsatisfactory with both fouling and hydro lysis dominating at times, although operating conditions for the membr anes were not always ideal. The precise cause(s) for the membrane degr adation was not established, but a mechanism for fouling (based upon t he presence of turbidity in the mine water) and a hypothesis fora poss ible cause of hydrolysis (alluding to the presence of radionuclides in the mine water) were proposed. Product water from the SPARRO process has an estimated gross unit cost (including capital costs) of 383 c/m( 3) (1994).