Single Process Arsenic and Antimony Removal Using Coagulation and Microfiltration

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1 Single Process Arsenic and Antimony Removal Using Coagulation and Microfiltration Presented by: Joe R. Tamburini, PE H.C. Liang, PhD Sam J. Billin, PE October 18, 2010 Tailings and Mine Waste 10

2 Outline Project Overview Arsenic Removal Technologies and Applications Coagulation-assisted microfiltration Arsenic and Antimony Chemistry Ferric Hydroxide Chemistry Bench Scale Test Results Full Scale Implementation Process flow description

3 Background on Project Location Nome, Alaska Water Source Gold mine dewatering wells Issues Elevated arsenic, antimony, and manganese Arsenic removal well understood, but antimony removal chemistry largely unknown Manganese issue developed after startup Hypothesis Coagulation-assisted microfiltration, ph adjustment

4 Arsenic Treatment Technologies Media Adsorption Granular iron oxide media Aluminum oxide media Ion Exchange Coagulation/Sedimentation/Filtration Coagulated-Assisted Microfiltration Reverse Osmosis

5 Arsenic Treatment Technologies

6 Coagulation and Microfiltration Iron Coagulants Ferric chloride Ferric sulfate, ferrous sulfate Ferric Salts Become Ferric Hydroxide FeCl 3 + H 2 O Fe(OH) + 2 (at ph < 7.3) Oxidized Arsenic Adsorbs to Ferric Hydroxide H 2 AsO 4- + Fe(OH) 2+ Precipitant Microfiltration Removes Precipitant

7 Coagulation and Microfiltration Schematic Representation of the Chemistry Arsenic (III) Oxidant As Fe(OH) 2 + As(III) OCl - As As - As(III) As(V) No Attraction Creates Negatively Charged As(V) Arsenic (V) As - As(V) Fe(OH) 2 + Chemically Bound to Ferric

8 Arsenic Treatment Technologies

9 Arsenic Treatment Technologies

10 Background on Project Water Quality Data Parameter Well 1 Well 2 Well 3 MCL Alkalinity, mg/l N/A ph, s.u N/A TDS, mg/l N/A Antimony, ug/l Arsenic, ug/l

11 Arsenic and Antimony Chemistry

12 Stability Diagram for As Speciation Stability diagrams also called Pourbaix Diagrams

13 Stability Diagram for As Speciation For optimal As removal, oxidize uncharged arsenic(iii) to charged arsenic(v) species

14 Stability Diagram for Sb Speciation

15 Stability Diagram for Sb Speciation Similarly to As, antimony must be in the Sb (V) oxidation state before it can be adsorbed by ferric hydroxide

16 Ferric Hydroxide Speciation 50% 7.3

17 Bench-Scale Study Parameters Solution ph Adjusted between 4.0, 5.0, 6.0 and natural ph Ferrous Sulfate Dose Adjusted between 10 and 160 mg/l Oxidant NaOCl Adjusted between 0 and 20 mg/l

18 Bench-Scale Results (Well 2) Antimony Conce entration (mg/l) FeSO4=80, NaOCl=20 FeSO4=120, NaOCl=20 FeSO4=120, NaOCl=10 FeSO4=120, NaOCl=0 FeSO4=160, NaOCl=20 MCL for Sb ph

19 Full-Scale WTP Optimization Optimum Operating Parameters Parameter Value Coagulant (Ferrous Chloride), mg/l 60 Oxidant (Sodium Hypochlorite), mg/l 10 ph, s.u. 6.0

20 Full-Scale WTP Results Effluent Sb Conc. (ug/l) MCL for Sb Ferric Chloride Dose (mg/l)

21 Full-Scale Implementation Raw Water Tank FeCl 3 Polymer Plate Settlers NaOH Treated Water Tank To Injection Wells Tailing Storage Facility Calcium Hypochlorite Reaction Tank NaOCl (if needed) Microfilter Membranes Waste Sump

22 Full-Scale WTP Results Effluent Mn Conc (ug/l) Manganese Removal MCL for Mn

23 Full-Scale Implementation

24 Full-Scale Implementation

25 Full-Scale Implementation

26 Project Conclusions Arsenic and antimony can be removed simultaneously using coagulation/microfiltration Effective arsenic removal was readily apparent Effective antimony removal improved with decreasing ph and increasing coagulant values A high coagulant dose was required for antimony removal Manganese removal dependant on effluent ph and ORP Manganese removal required adequate residence time

27 Questions??

28 Bench-Scale Results (Well 2) 100% 90% 80% FeSO4=80, NaOCl=20 FeSO4=120, NaOCl=20 FeSO4=120, NaOCl=10 FeSO4=120, NaOCl=0 FeSO4=160, NaOCl=20 Antimony Removal 70% 60% 50% 40% 30% 20% ph

29 Bench-Scale Study Procedure Filled 4 Beakers with Raw Water Added Oxidant Sodium Hypochlorite (bleach) Adjusted ph Used sulfuric acid Added Coagulant Varied dose on each test run Repeated procedure for several coagulant doses with each of three raw water sources

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