Electrocoagulation Treatment of Heavy Metals from Mine Impacted Water Denney Eames, P.E. & Jacob Aylesworth, EIT IWC 16-45

Executive Summary Electrocoagulation (EC) introduction History of the technology Overview of the science of electrochemistry Review three mine water treatment case studies for EC treated water Underground mine dewatering Tailings stormwater runoff Smelter environmental cleanup water Review the capital and operational costs associated with these treatment process

Introduction to Electrocoagulation First patented in 1906 by A. E. Dietrich Original patent was used to treat bilge water from ships Multiple attempts have been made to commercialize the technology with varying degrees of success

Electrocoagulation Today Electrocoagulation is used in many industries today Stormwater treatment Environmental remediation Marine Pollution prevention Automotive cleaning Food and beverage Mining Oil & gas

Electrocoagulation Process The electrical current releases positively charged metal ions that attract a disproportionate quantity of negatively charged contaminants Small particles agglomerate into larger particles through precipitation and absorption Gas generated at the cathode assists in separating the lighter coagulated particles and forming a stable floc

Fe3+ Fe3+ Fe3+ OH- HM CL- CL- OH- OH- OH- CL- CL- CL- HM OH- OH- HM

Cathode Anode + Fe3+ Fe3+ Fe3+ OH- Cathode HM OH- OH- Fe3+ H2 HM OH- OH- Fe3+ HM H2 OH- Less Competition, Higher Potential Energy

Electrocoagulation Effects Electrocoagulation Makes Particles Larger Gravity/Floatation Separation Electrocoagulation

Electrocoagulation Targets 1. Coagulation of suspended solids 2. Precipitation and agglomeration of dissolved metals 3. De-emulsification of oil and grease from water

Literature Chemical Treatment Electrocoagulation “Alum, lime and/or polymers…tend to generate large volumes of sludge with high bound water content that can be slow to filter and difficult to dewater. These treatment processes also tend to increase the total dissolved solids (TDS) content of the effluent, making it unacceptable for reuse within industrial applications.”* Electrocoagulation “The characteristics of the electrocoagulated floc differ dramatically from those generated by chemical coagulation. An electrocoagulated floc tends to contain less bound water, is more shear resistant and is more readily filterable”** *Benefield, Larry D.; Judkins, Joseph F.; Weand, Barron L. (1982). Process Chemistry for Water and Wastewater Treatment. Englewood Cliffs, NJ: Prentice-Hall. P. 212. **Woytowich, David L.; Dalrymple, C.W.; Britton, M.G. (Spring 1993). “Electrocoagulation (CURE) Treatment of Ship Bilge Water for the US Coast Guard in Alaska”. Marine Technology Society Journal (Columbia, MD: Marine Technology Society, Inc.) 27(1):92.

Project Process Flow

Mine Water Underground Mine Dewatering Treated at mine surface 30 days @ 250 gpm Elevated cadmium, copper, arsenic, lead

Data: Underground Mine Dewatering Analytical Parameter Average ug/L Standard Deviation Max/Min INF EFF % Reduced Cd 2.1 0.54 74.5% 0.44 3.7/1.4 1.7/0.14 Cu 22 1.7 92.6% 3.5 1.3 32/16 6.3/0.10 Pb 105 1.4 98.6% 15 1.1 141/60 5.4/0.55 Zn 531 70 86.9% 73 62 660/390 244/10 pH 8.1 0.0% 0.2 8.3/7.9 # of Samples 27  Total Treated Volume: 2,628,600 gallons

Tailings Stormwater Runoff Mine water storage pond 25 days @ 250 gpm Elevated cadmium, copper, arsenic, lead

Data: Tailings Stormwater Runoff Analytical Parameter Average ug/L Standard Deviation Max/Min INF EFF % Reduced Cd 0.44 0.20 55.5% 0.33 0.15 1.3/0.13 0.61/0.03 Cu 4.4 1.6 64.3% 0.29 9.3/2.8 2.1/1.1 Pb 27 0.48 98.2% 14 0.40 58/12 2.3/0.18 Zn 130 89.1% 32 6.9 242/104 37/5.6 pH 8.0 0.0% 0.2 8.2/7.8 # of Samples 23  Total Treated Volume: 1,930,200 gallons

Smelter Site Environmental Cleanup Water Mine water storage pond 12 days @ 100 gpm Elevated cadmium, copper, arsenic, lead pH treatment (raised to 8.6 after EC)

Data: Smelter Environmental Cleanup Water Analytical Parameter  Average ug/L Standard Deviation Max/Min INF EFF % Reduced Cd 2,654 12 99.5% 1,755 9.1 7,107/864 34/6 Cu 216 3.8 98.2% 211 1.0 772/34 6/3 Pb 39,932 37 99.9% 40,594 27 147,959/ 3,341 105/6 Zn 10,472 36 99.7% 5,465 17 22,981/ 2,212 58/15 pH 7.6 8.6 -13.1% 0.3 7.9/7.3 8.9/8.3 # of Samples 10 Total Treated Volume: 375,900 gallons

Capital Costs 6,000 gpm: Water Treatment Plant Capital Cost Item Cost Engineering $425,000 Process Equipment $8,624,000 Facility, Infrastructure & Installation $2,493,000 Management, Supervision & Commissioning $357,000   Total $11,899,000

Operational Costs for a 6,000 gpm: EC Water Treatment Plant Operational Cost Item $/1000 gallon Annual Cost* Consumables (EC Cells, UF Membranes, Misc.) $1.252 $3,255,200 Power ($0.07/KWH) $0.272 $707,200 Operations Labor $0.162 $421,200   Total $1.686 $4,383,600 * Estimated annual cost based on treating 2.6 billion gallons per year

Operational Costs for a 6,000 gpm: Chemical Water Treatment Plant* Operational Cost Item $/1000 gallon Annual Cost* Consumables (Chemicals, Filters, Misc.) $0.879 $2,285,400 Power ($0.07/kWh) $0.215 $559,000 Operations Labor $0.162 $421,200   Total $1.256 $3,265,600 Note: Capital cost range was estimated at $10,300,000 to $15,700,000 * Estimated annual cost based on treating 2.6 billion gallons per year

Conclusions Capital cost for an EC and chemical plant were equivalent EC advantages Full compliance demonstrated in heavy metal reduction Passed all aquatic toxicity testing Reduced sludge/tailings production EC disadvantage cell cost 34% higher operational cost compared to chemical The cost of the EC cell was the majority of the cost Designing a less expensive EC cell is the key to lowering operational costs