Collection, treatment and re-use of mine water in the Olifants River Catchment

Mine water in the Upper Olifants River Catchment in Mpumalanga (upstream of Loskop Dam) is at times discharged into local streams, resulting in local acidification and regional salination of surface water resources. Pollution of surface water can be prevented by collecting and heating mine water to a quality where it could be re-used without restriction (Cleanwater 2020 In itiative). Mine water in the Olifants River Catchment currently amounts to only 4,6% of the total water usage, but contributes 78,4% of the sulphate l oad. Limestone and lime treatment is the most cost-effective technology for neut ralization and partial sulphate removal of acidic/sulphate-rich water to su lphate levels of less than 1500 mg/l due to precipitation of magnesium and removal of the associated sulphate fraction (through gypsum crystallization ). Neutralized mine water of this quality may be suitable for irrigation. A number of alternative desalination treatment technologies were investigate d (subsequent to gypsum crystallization pre-treatment) where treated mine w ater must meet more stringent quality requirements (e.g. less than 200 mg/l SO4). The capital cost of these processes varied between R4 million/(Ml/d) and R10 million/(Ml/d) and the running cost between R2/m(3) and R5/m(3). Water usage in the Upper Olifants River Catchment currently amounts to 947 Ml/d (including the power stations), and wilt increase to an estimated 1385 Ml/d by 2020. The additional water demand by 2020 (438 Ml/d) will have to be supplied by importation from neighbouring catchments, and more efficient utilization of the local water resources, including excess mine water. Var ious levels of treatment are required to make mine water suitable for the f ollowing potential applications (acceptable treated water sulphate concentr ation shown in brackets): irrigation (2000 mg/l), coal processing plant (10 00 mg/l),general industrial use (500 mg/l), discharge to public streams (50 0 mg/l), potable use (200 mg/l) and cooling water in power stations (20 to 40 mg/l). The following two options, or a combination thereof can be consid ered for management of excess mine water in the Upper Olifants River Catchm ent: Collection and treatment of excess mine water to a quality suitable for sel ected urban and industrial applications (Option A). Collection and treatment of mine water to a quality suitable for irrigation (Option B). The estimated capital and running cost For Option A amounts to R528.5 milli on and R55.7 million/year, respectively, compared with R68,2 million and R1 1,9 million/year for Option B. It is recommended that Option B be investiga ted for implementation in the short to medium-term. Option B was selected d ue to cost benefits and the initial favourable results obtained by a joint Water Research Commission and Coal Industry initiative where mine water is used for irrigation. Option A may become feasible in the long-term to ensur e maximum environmental protection acid reduced treatment cost as a result of anticipated technological improvements over the next 5 to 10 years.