Innovations and Demonstration of Novel Mine Water Treatment Technologies Dr Jo Burgess Research Manager: Mine Water Treatment and Management Water Research Commission

What is the current standard method? 2 High Density Sludge (HDS) process, followed by conventional reverse osmosis (RO).

Water Type  Acidic; Sulphate; Calcium; Manganese Neutralisation Desalination Solid Gypsum Byproduct 180 tons/day Liquid Waste – Brine 0.09 Ml/day Treated Water 30 Ml/day Up to 99.3 % water recovery but not enough …….. Hi recovery Precipitating Reverse Osmosis (HiPRO) process 3

HDS process, followed by conventional RO 4 Disadvantages Multiple reaction stages and extended retention times, with associated high capex. High quantities of iron hydroxide and gypsum sludge created, no direct value, require disposal. Smaller volumes of complex, hazardous brine created, require disposal / treatment (e.g. eutectic freeze crystallisation) Lime demand is high, with associated high opex. The energy demand is high, with associated opex. Highly engineered process. HDS product water quality does not meet environmental or potable specifications, further treatment required. Advantages Established, in operation for many years, well understood. Can adapt to variable AMD quality and quantity. Product water is potable quality. The only process that has been installed at full scale in RSA. The capacity of both HDS and RO treatment plants can be increased modularly.

Eutectic Freeze Crystallization R&D to Fundamental principles. Novel Technology for Recovery of Water and Solid Salts from Hypersaline Brines: Eutectic Freeze Crystallization. Batch system. Model solutions. Lab scale. (K5/1727) 2010 to Working concept. Extended Investigations into the Recovery of Water and Salts from multi- component Brines. Real wastewaters. Batch system. Lab scale. (K5/2012) 2013 to Continuous Eutectic Freeze Crystallization. Scale up. Real wastewaters. Continuous process. Pilot scale. Demo plant in collaboration with industry research association (Coaltech 2020). (K5/2229)

20 Temperature[˚C] Concentration [Wt %] Ice + Aqueous solution Salt + Aqueous solution Ice + Salt Eutectic point 40˚C 20˚C 0˚C -20˚C -40˚C -60˚C Ice Salt Principle of Eutectic Freeze Crystallization

7 Temperature(°C) 20 Na 2 SO MgSO Component Not to scale KCl NaCl ice Recovery of pure salts Recovery of pure water Extreme waste minimisation Na + Mg 2+ K + SO 4 2- Cl - Selective recovery of salts

Demo plant at Optimum Colliery 8 Slurry skimmer Clean water

What are our other options? 9 Phase 1 Irrigation with concomitant soil amendment Pump AMD to surface from ECL Pre- treatment (HDS) Domestic supply system Irrigation Full active treatment Pump AMD to surface from depth Phase 0Phase 4Phase 3

Pumping AMD for active treatment 10 Alternative treatment technologies were all rejected on the basis of insufficient information regarding their application at full scale. “In the evaluation of the technologies, it needs to be taken into account that the AMD problem on the Witwatersrand is currently the biggest Acid Mine Drainage problem globally. Nowhere have plants been constructed to meet such a demand as is required on the Witwatersrand and South Africa is currently embarking on untested territory in this regard... It will therefore be advisable to test the alternative technologies that show potential at demonstration scale to assess all risks.”

Electrocoagulation 11

Ettringite precipitation 12

Alternative RO 13

VitaSOFT process 14

Biological sulphate reduction: the VitaSOFT process 15

Pacques process 16

Agricultural use of mine drainage 17 Can be achieved by pumping the AMD to surface and then either HDS process & use product water for irrigation, or irrigating with the untreated AMD and concurrently adding soil amendments as a bulking and pH correcting agent. The latter releases us from the need for AMD treatment plants in some areas (depends on land availability). University of Pretoria’s Department of Plant Production and Soil Science has provided clear proof of concept that land treatment, either with mine tailings and/or a clay soil, suitably amended with fine limestone or fly ash from power stations, is technically attractive and could offer solutions to two environmental challenges at once: erodible mine tailings and large volumes of contaminated mine water.

Agricultural use of AMD 18

Deep level pumping concept 19

Further information 20 WRC website: Jo Burgess: Mine water research brochure Summary report Knowledge Review Project research reports