Pass the salt recovery of water & salts from mining brines using Eutectic Freeze Crystallization

Transcription

1 Pass the salt recovery of water & salts from mining brines using Eutectic Freeze Crystallization Dyllon Randall IOM 3 Young Person s World Lecture Competition 2011 São Paulo, Brazil 29 September 2011

2 Acid Mine Drainage oxygen + water + sulfide = sulfuric acid

3 Brine Production AMD Treatment Brine

4 Brine Production Coal & Gold tons/day 1170 tons/day Chris Waygood,2008

5 South Africa s brine disposal strategy Lined evaporation ponds Mechanical evaporators Disposal to ash systems

6 Phase change desalination Phase change desalination technique H 2 O(l) Evaporation H 2 O(g) H 2 O(l) Freezing H 2 O(s)

7 kj/kg Is freezing not expensive? 2500 ΔH vap Producing CuSO 4 5H 2 O from a freeze crystallization process requires 65% less energy than a 3 stage evaporation process (van der Ham, 1999) 500 ΔH fus 0 Evaporation Freezing

8 The treatment balance Liquid Solid

9 Eutectic Freeze Crystallization

10 Impurities are excluded from ice

11 Ice floats, salt sinks

12 No added chemicals

13 Corrosion is minimised

14 How does Eutectic Freeze Crystallization work? Temperature( o C) Ice 25 o C Liquid + Liquid Salt + Liquid Eutectic Point + Salt Concentration(wt%)

15 Temperature( C) EFC for complex systems 20 Na + Mg 2+ K + SO 2-4 Cl - Recovery of pure salts Recovery of pure water Extreme waste minimisation -1.3 ice Not to scale Na 2 SO 4 10H 2 O MgSO 4. 11H 2 O Component KCl NaCl 2H 2 O

16 Brine treatment protocol. Brine analysis 2. Thermodynamics 3. Kinetics

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18 The Hi Recovery Precipitating Reverse Osmosis (HiPRO)

19 The emalahleni Water Reclamation Plant currently produces m 3 /d potable water, 100 t/d solid waste and 150m 3 /d liquid waste.

20 Solid waste solid waste GypSLIM GypBump Sulfur, Limestone, Magnesite. Building, Mining Products.

21 Gypsum house

22 Liquid waste A Real Brine

23 mg/l Step 1: Brine analysis A Real Brine Na + K + Ca 2+ Mg 2+ NH 4 + SO 4 2- Cl - NO 3 - HCO 3 -

24 Ion imbalance Temperature C 22 Conductivity ms/cm 22.2 ph Density g/cm Concentration Molality mg/l mmol/l meq/l Na K Ca Mg NH SO Cl NO HCO Total Cation meq/l Total Anion meq/l Imbalance % 5.766

25 Step 2: Thermodynamics Electrolyte thermodynamic software Calculate equilibrium conditions Mixed Solvent Electrolyte (MSE) databank

26 Salt (g/l) Water (g/l) Step 2: Thermodynamics CaSO 4 2H 2 O KCl Na 2 SO 4 10H 2 O H 2 O Temperature ( C) 0

27 Step 3: Kinetics seed crystals 22 C -0.9 C Brine

28 Step 3: Kinetics ice + salt(s)

29 STAGE 1 STAGE 2 STAGE 3 Results Ice Ice + CaSO 4 2H 2 O FEED 54% 71% 82% 85% 91% Ice + Na 2 SO 4 10H 2 O 93% 96% 100% 50% 0 50% 100%

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31 Concentrating (mg/l) Ice purity Na + Ca 2+ Mg 2+ K + Cl - SO No Washes 1 Wash 2 Washes 3 Washes

32 Concentrating (mg/l) Ice purity Na + Ca 2+ Mg 2+ K + Cl - SO No Washes 1 Wash 2 Washes 3 Washes

33 With EFC, the emalahleni Water Reclamation Plant can achieve 99.95% water recovery & reduce its current liquid waste stream by 96%

34 Preliminary cost estimates Eutectic Freeze Crystallization Cost per m 3 water treated (full-scale plant) $1.3 Capital Cost Estimate (pilot plant) $ Operating Cost Estimate per annum (pilot plant) $

35 The hybrid process Water Feed RO EFC STAGE 1 EFC STAGE 2 Waste recycle Na 2 SO 4 10H 2 O CaSO 4 2H 2 O

36 Conclusions A brine can be treated using EFC, Potable water, pure calcium sulphate and pure sodium sulphate can be produced, The purity of the ice formed can be improved with washing, A 99.6% overall conversion could be obtained if EFC was adopted in the EWRP, The cost of an EFC plant is estimated at $1.3/m 3 of treated water.

37 Final thoughts EFC is an exciting new technology but it still has a long way to go before it is fully accepted, The notion of a waste must not be tolerated and the ultimate goal should be zero waste, A brine should be viewed as a resource rather than a waste, Waste treatment should be at the expense of company profits, if need be, but never at the expense of the environment or our scarce water resources.

38 In an age when man has forgotten his origins and is blind even to his most essential needs for survival, water along with other resources has become the victim of his indifference Rachel Carson

39 Acknowledgements Anglo Coal Water Research Commission of South Africa University of Cape Town Research Associateship Award (2010)

40 Thank You