Approaches to Treatment of Very High Acidity Wastewater

Transcription

1 Approaches to Treatment of Very High Acidity Wastewater AIChE International Society for Water Solutions Industrial Water Use and Reuse Workshop Strategies for Sustainable Water Management for Mining Kevin W. Conroy, PE

2 Presentation Summary Project Background Treatment Options Process Development Testing Process Optimization Testing Conclusions Disclaimer: The Presenter was involved with this Project while employed with another firm, and the Project discussed in this presentation is not the direct work of Tetra Tech 2

3 Project Background 1

4 Project Location

5 Site Layout 5

6 Project Background Operating polymetallic mine (lead, zinc, silver) Significant quantity of mining influenced water Currently treat ~2,800 gpm (630 m 3 /hr) Need to expand treatment to ~6,000 gpm (1,375 m 3 /hr) Total of seven individual sources to be treated Conventional lime treatment system used to treat existing sources Lime cost with expanded facility was of concern originally projected as a potential 3x increase in chemical cost 6

7 Sources Source Current Flow Future Flow Underground Mine 85.7% 49.8% Pampa Seca Stockpile 1.7% 1.8% Rumiallana Stockpile 5.7% 13.1% Open Pit 1.2% 2.6% Paragsha Industrial Zone 5.7% 5.2% Other Stockpiles 0.0% 2.6% Quiluacocha Tailings Pond Excelsior Stockpile 0.0% 24.8% 7

8 Chemistry, General Parameters Parameter Units Underground Mine Pampa Seca Rumiallana Open Pit Paragsha Other Stockpiles Quilulacocha ph SU TSS mg/l TDS mg/l 10, ,000 17,000 1,300 11, ,000 26,000 Acidity mg/l 4, ,000 1, ,000 4,300 8,500 Sulfate mg/l 8, ,000 13, , ,000 30,000 Current Flow Future Flow % 85.7% 1.7% 5.7% 1.2% 5.7% 0% 0% % 49.8% 1.8% 13.1% 2.6% 5.2% 2.6% 24.8% 8

9 Chemistry, Metals Parameter Units Underground Mine Pampa Seca Rumiallana Open Pit Paragsha Other Stockpiles Quilulacocha Arsenic mg/l Cadmium mg/l Chromium mg/l Copper mg/l 87 1, , Iron mg/l 1,200 41, ,000 2,900 Lead mg/l Manganese mg/l 140 1, , Mercury mg/l <0.002 <0.002 <0.002 <0.002 <0.002 <0.002 <0.002 Nickel mg/l Zinc mg/l 400 3, , Current Flow % 85.7% 1.7% 5.7% 1.2% 5.7% 0% 0% Future Flow % 49.8% 1.8% 13.1% 2.6% 5.2% 2.6% 24.8% 9

10 Water Quality Variability 10

11 Water Quality Summary and Discharge Limits General Chemistry Metals (dissolved) Parameter Units Influent LMP Standards ECA Standards Sulfate mg/l 27, TSS mg/l ph SU Aluminum mg/l Arsenic mg/l Copper mg/l Iron mg/l 3, Lead mg/l Manganese mg/l Nickel mg/l Zinc mg/l

12 Treatment Options 12

13 Treatment Options Base Case: Conventional lime treatment, expansion of the current water treatment plant configuration. Other options Lime High Density Sludge (HDS) Limestone/Lime High Density Sludge Copper Recovery/Lime High Density Sludge 13

14 Lime High Density Sludge Relies on insolubility of heavy metals in the presence of elevated hydroxide ions Widely implemented and established solution for ARD waters Tested with and without oxidation Sludge recycle can result in better chemical utilization and denser sludge 14

15 Lime High Density Sludge 15

16 Limestone/Lime High Density Sludge Advantages Lower material costs Can create denser sludge Disadvantages Longer reaction times Low utilization due to sulfate armoring Inability to raise ph above 6.0 in a single step 16

17 Metals Recovery High metals values made this a possible option to offset some portion of the treatment costs Considered a range of options including sulfide precipitation, ion exchange, solvent extraction and electrowinning Sulfide precipitation was selected for evaluation as it is already the technology used for metals recovery Approach was to remove/recover copper followed by lime treatment for the balance of the metals Primary concern was a clean separation of copper from arsenic Copper recovery was a pretreatment step for the two highest concentration sources (Pampa Seca and Other Stockpiles) 17

18 Process Development Testing

19 Process Development Test Program

20 Jar Testing 20

21 Lime Titrations Complete a series of basic lime titrations Lime dose determined to be 10 to 11 gr/l Three hour reaction time required ph 8.1, achieved all goals except: LMP standard for zinc (83 mg/l versus 1.5 mg/l) ECA standard for sulfate (4,900 mg/l versus 500 mg/l) ECA standard for manganese (73 mg/l versus 0.2 mg/l) ph 9.6, achieved all goals except: LMP standard for zinc (29 mg/l versus 1.5 mg/l) ECA standard for sulfate (3,800 mg/l versus 500 mg/l) ECA standard for manganese (4.3 mg/l versus 0.2 mg/l) 21

22 Lime Titrations with Oxidation Complete an additional series of lime titrations with oxidation Oxidation did generally lower the lime dose a bit Very close to theoretical demand -> high utilization ph 8.2, achieved all goals except: ECA standard for sulfate (4,800 mg/l versus 500 mg/l) ECA standard for manganese (26 mg/l versus 0.2 mg/l) ph 10.6, achieved all goals except: LMP standard for arsenic (0.3 mg/l versus 0.1 mg/l) LMP standard for iron (20 mg/l versus 2 mg/l) ECA standard for sulfate (2,100 mg/l versus 500 mg/l) ECA standard for manganese (1.0 mg/l versus 0.2 mg/l) No explanation on the arsenic and iron results 22

23 Limestone/Lime Titrations Maximum ph at about 5.8 at a limestone dose of 10 gr/l Very close to theoretical demand -> high utilization Much lower lime dose was required to get to the ph 8.1 with limestone pre-neutralization 10 gr/l lime 10 gr/l limestone + 3 gr/l lime Reaction time significantly reduced 30 minutes for limestone stage 30 to 60 minutes for lime stage Theory CO 2 gas bubbles break up gypsum particles (preventing limestone coating) and promote better mixing 23

24 Copper Recovery Multiple challenges Very high lime demand 75 gr/l to get to ph 4.66 Solids management Very viscous, difficult to mix Poor settling Minimal liquid after two hours Two morphologies red, slimy material and thick black granular material Non-selective copper removal 99.4% removal of copper (initial concentration of 1,996 mg/l) Significant arsenic removal also observed Copper recovery abandoned as an option 24

25 Process Optimization Testing

26 Solids Recycle Testing Settling Curves 26

27 Solids Recycle Testing Underflow Solids 27

28 HDS Performance Parameter Units Treatment Goal Influent Blend HDS 10 Recycles With Oxidation ph SU Lime Dose g/l Ca(OH) Sulfate mg/l ,000 3,100 1,400 Aluminum mg/l <0.1 <0.1 Arsenic mg/l <0.015 <0.015 Cadmium mg/l <0.005 <0.005 Copper mg/l <0.015 <0.015 Iron mg/l 2 3,300 <0.1 <0.1 Lead mg/l <0.009 <0.009 Manganese mg/l Nickel mg/l <0.04 <0.04 Zinc mg/l

29 Limestone/Lime Performance Parameter Units Treatment Goal Influent Blend R-1 R-3 R-6 ph SU Limestone g/l Ca(OH) Lime g/l Ca(OH) Sulfate mg/l ,000 4,700 2,600 1,700 Arsenic mg/l Cadmium mg/l Copper mg/l Iron mg/l 2 3, Lead mg/l Nickel mg/l Zinc mg/l

30 Conclusions

31 Conclusions Compliance HDS and Limestone/Lime both meet LMP standards at a ph in the 8 to 8.5 range HDS can meet ECA standard for manganese at a high enough ph with oxidation Sulfate minimized to saturation concentrations at high enough ph Reduced Capital Cost Lower reaction times and tank sizes with Limestone/Lime Reduced Operating Costs HDS: estimated 10-20% reduction Limestone/Lime: estimated 35% reduction 31

32 Thank You! Questions 32