Arsenic Removal From Aqueous Systems. Lucas R. Moore, Ph.D. Marcelo Costa Ph.D. Jorge Langsch Laura Sanders Jean Robert Durand

Transcription

1 Arsenic Removal From Aqueous Systems Lucas R., Ph.D. Marcelo Costa Ph.D. Jorge Langsch Laura Sanders Jean Robert Durand

2 Arsenic In natural water As +3 and As +5 - inorganic compounds: As +3 60x > As +5 Toxicity of Arsenic Species - inorganic compounds > organic compounds - organic compounds: As +3 > As +5 World Health Organization As < 10 μg/l Arsenic is listed in at least 1149/1684 sites on the EPA National Priorities List 0.8 g As/t Earth s crust Generally combined with sulfur and oxide ores Sulfides: Orpiment: As 2 S 3 Algar: AsS with iron: FeS 2, FeS, FeAsS, CaFeS 2 Oxides Arsenolite: As 4 O 6 Rarely in it s elemental state (gray metallic crystals)

3 Arsenic: Health Effects ***Highly Toxic -Chemically similar to the other pnictogens Sources of Exposure Natural Industrial Dissolution of minerals Fossil Fuels Volcanic activity Pesticides Timber Treatment Metal Smelting Symptoms of Arsenic Poisoning Peripheral neuropathy Hair loss Gastrointestinal symptoms Skin lesions Diabetes Head Aches Cardiovascular disease Diarrhea Cancer Vomiting Cramping muscles Death Leukoncychia Many Others

4 World Areas with Arsenic Contamination Problems Natural Groundwater: Taiwan, Chile, Mexico, Argentina, India, USA, New Zealand, Poland, Spain, China, Srilanka, Canada, Bangladesh, Hungary, Japan, and much more. Coal Burning: Mexico and former Czechoslovakia Metal Processing: Japan, Australia, India, Canada, Greece, Ghana, USA, Rhodesia, Sweden, Bulgaria, and more Country USA EUA Brazil Chile Bolivia Peru Ecuador Argentina Mexico Columbia Venezuela Paraguay Discharge Limit 10 μg/l 10 μg/l 0.2 mg/l 0.5 mg/l 1.0 mg/l 0.5 mg/l 0.1 mg/l 0.5 mg/l 0.75 mg/l 0.5 mg/l 0.5 mg/l 0.5 mg/l IN ALL THESE COUNTRIES Effluents must be treated in order to meet discharge criteria

5 Cradle to Desired Grave! Where do you want the arsenic to end up? Grave (The End) Untreated water Allowed to enter environment Held in a lined pond Treated Chemical (arsenic is contained in sludge) Tailings Facility (monitored for decomposition/leaching) Used as back-fill (Only if stable) Physical (concentrated in solution) Sell for commercial use Pesticide (Wood Products) Herbicides Insecticides Dopant in Semiconductor Electronic Devices Copper and Lead Alloy Strengthening (Car Batteries)

6 Leachability To lose or cause a loss in soluble substances As it applies to Mining The ability of a treatment to maintain the immobility of the contaminant. TCLP: Toxic Characteristic Leaching Procedure A predictive tool used to classify solid waste in terms of sludge stability and tailings storage requirements EPA Method 1311: Evaluates leachability of contaminants at ph 4.93 and 2.88, adjusted with acetic acid with 18 (+ 2) hours of contact time. This method evaluates the sensitivity of acidic ph on the leaching, but doesn t take into account other environmental redox (chemically or microbial) conditions or leaching over an extended amount of time.

7 Is the Redox System Important? Much more toxic (The oxidation states of concern for mining applications) Oxidation (Aqueous Systems) Elemental forms are relatively insoluble (Treatment is easy) Elemental (Rarely Found in Nature) Complexed forms are less toxic, but under acidic conditions a gas can be generated, which is extremely toxic. Naturally Occurring

8 Physical Treatment

9 General Treatment Schematic (Chemical Treatment) Raw Water Treatment Oxidation Mix Tank Flocculants Effluent Treated Thickener Lake/River Residue Land field

10 In a time long ago Lime Treatment Typical Mineral Scale Ksp (BaSO 4 ) = 1.08 X Ksp (Calcite) = 3.8 X 10-9 Ksp (aragonite) = 6.00 X 10-9 Ksp (Ca 3 (PO 4 ) 2 ) = 2.07 X Ksp (As 2 S 3 ) = 1 X Ksp (Ca-Arsenate)= 6.8 X 10-19

11 EPA s Listed Best Demonstrated Available Technology Ksp = 5.7 x 10-21

12 Why Change? Yes No -Chemical Consumption -Logistics -Process Sensitivities -Slurry pond construction cost -Available space for slurry pond -Sludge Stability -Sludge Volume -Production Rate -Cost

13 Do you need a change? I. Must achieve regulated discharge limit II. III. IV. amount of residue Stability Leaching EPA test methods Costs $/m³ Stability of Fe/As Sludge ph = 4.9 Preatrement Leached (ppm) Caustic 19 Lime 13.2

14 Chemisorption (IP-1*)

15 Technology Comparison: Arsenic Removal (Synthetic Water) IP-1* = < 5ppb IP-1* with 1500 ppm sulfate = 7 ppb TCLP (EPA 1311) = None Detected EPA discharge limit = 10 ppb

16 Technology Comparison: Sludge Volume (Initial 12 ppm As(V)) IP Fe Wet Cake IP Wet Cake Mass (g) Dry Cake Mass (g) Solids in Wet Cake (%) 33 Fe Wet Cake Mass (g) Dry Cake Mass (g) Solids in Wet Cake (%) 10

17 Metal Mine NA-1: Arsenic Ore Processing Mine Oxidation Ferric Dewatering Discharge

18 Metal Mine NA-2: Arsenic Ore Processing Mine Dewatering Oxidation Ferric Discharge

19 Metals Mine NA-2: Process Requirements Particle Size Requirements: um

20 Where are we in the development? 1 2 Current Status 3 4 Concept Technology Developed Synthetic Water Technology Optimization Evaluation in Mine Waters Understand Process limitations Scale up sensitivities and product adjustment Full scale Project Evaluation Development Pilot Trials Commercialization

21 What else can this adsorbent do? Contamimant Initial Concentration (ppb) Final Concentration (ppb) Mine Water (Se) 100 < 5.0 ppb Arsenic 25,500 < 5.0 ppb Mine Water (As) 42 < 5.0 ppb Zinc 697 < 10.0 ppb Phosphorus 603 < 3.0 Mine Water (P) 26, Cadmium 11,000 < 0.5 Mine Water (Cd) 8,300 < 0.2

22 Conclusions A novel adsorption technology is under development that incorporates both physical and chemical treatment methods. This technology has been shown to be efficient at reducing As concentrations to levels below the regulated limits on lab scale evaluations. The sludge generated has demonstrated increased stability, which passes the US EPA s leachability requirements. Sludge volumes generated was significantly less than common commercially available technologies. The treatment system is diverse and can be tailored to achieve the contaminant levels desired. The system has proven effective on the lab scale in actual mine process waters even in the presence of TDS, as well as other cations and anions that may pose a limiting factor in other treatments (e.g. Ca 2+, Cl -, and SO 4 2- ).

23 Thank you! Gracias! Obrigado! Kiitos! Xie xie! Merci!