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
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
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
Arsenic Treatment Technologies Media Adsorption Granular iron oxide media Aluminum oxide media Ion Exchange Coagulation/Sedimentation/Filtration Coagulated-Assisted Microfiltration Reverse Osmosis
Arsenic Treatment Technologies
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
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
Arsenic Treatment Technologies
Arsenic Treatment Technologies
Background on Project Water Quality Data Parameter Well 1 Well 2 Well 3 MCL Alkalinity, mg/l 200 262 172 N/A ph, s.u. 7.7 7.6 7.9 N/A TDS, mg/l 324 410 232 N/A Antimony, ug/l 0.0 171 6.0 6 Arsenic, ug/l 79 205 155 10
Arsenic and Antimony Chemistry
Stability Diagram for As Speciation Stability diagrams also called Pourbaix Diagrams
Stability Diagram for As Speciation For optimal As removal, oxidize uncharged arsenic(iii) to charged arsenic(v) species
Stability Diagram for Sb Speciation
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
Ferric Hydroxide Speciation 50% 7.3
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
Bench-Scale Results (Well 2) Antimony Conce entration (mg/l) 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 FeSO4=80, NaOCl=20 FeSO4=120, NaOCl=20 FeSO4=120, NaOCl=10 FeSO4=120, NaOCl=0 FeSO4=160, NaOCl=20 MCL for Sb 0.00 3.0 4.0 5.0 6.0 7.0 8.0 ph
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
Full-Scale WTP Results Effluent Sb Conc. (ug/l) 7 6 5 4 3 2 1 0 MCL for Sb 0 20 40 60 80 100 Ferric Chloride Dose (mg/l)
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
Full-Scale WTP Results Effluent Mn Conc (ug/l) 120 100 80 60 40 20 0 Manganese Removal MCL for Mn
Full-Scale Implementation
Full-Scale Implementation
Full-Scale Implementation
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
Questions??
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% 3.0 4.0 5.0 6.0 7.0 8.0 ph
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