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Simple water treatment before release to river (2 replies and 3 comments)
Hello Ianvallecera,
Well normally you would not let the Iron and Nickel go into the river, however Iron precipitates at a pH of 2.8 - 4.0 and Nickel from 8.0 to 10.5. you can use Calcium Hydroxide to bring up your pH or powdered Limestone but the limestone will not get your pH high enough to precipitate your nickel out. If you use Calcium Hydroxide and bring your pH to 10.5 most of your base metals will drop out as hydroxides
You could pump the water into a couple of reaction tanks to add which ever neutralizing agent you plan to use to raise your pH and let the overflow of the second reactor go to the river but that is not good for the environment although it is simple.
More information is needed as to what your desired result is.
What are your limits for Metals and pH discharge, you may need to press out the hydroxides prior to running the effluent to the river.
Wayne
HI,
just as a note... Iron will only precipitate at low pH if it of the correct Oxidation state. if not, you will need to add an Oxidation step in or push the pH >11.
Look up processes called "high density sludge" or Max-R. The Max-R is a good program if you are looking to thicken or Filter the precipitates produced. It can also help to reduce the lime expenditure and wastage.
Legislated discharge requirements, I assume apply to the discharge you are proposing? Using Canadian discharge requirements as an example (Metal Mine Effluent Regulation, MMER): Ni = 0.5 mg/L, TSS = 15 mg/L, Fe not specified in MMER, 96HourLC50 = 50% survival Rainbow Trout bioassay. In BC, Canada, the Fe limit would be based on dilution into the receiving stream and the BC Water Quality Criteria (BCWQC) for Fe; the limits for Ni and TSS would also be affected by the BCWQC. There are likely other metals in your effluent that will have legislated limits?
What comes to mind as a fairly simple water treatment is: adding alum, lime and flocculant and allowing the settlement after appropriate mixing/conditioning, and the “decant” can be discharged if it meets the regulatory limits. This procedure can be tested in your lab. The flocculant tested should have a 96HourLC50 (mg/L) which is relatively high so that residual flocculant does not cause a failure of the 96HourLC50 for the discharged effluent. Toxicity problems may potentially be caused by elevated Fe-hydroxide (undissolved) due to the positive charge induced by the Fe on the coagulant/flocculant particles (if they are present after clarification of the treated effluent). Also, worth bearing in mind that the cationic flocculants may have an adverse effect on discharge toxicity – best to search for a flocculant with a low toxicity. There are references on flocculants and toxicity in http://www2.gov.bc.ca/assets/gov/environment/waste-management/industrial-waste/industrial-waste/mining-smelt-energy/assessing_design_size_and_operation_of_sediment_ponds.pdf
The alum/flocculant procedure has been used extensively in potable water treatment – the residue resulting from this procedure will require a location for storage (e.g. tailings pond). The use of the alum forms an adsorption medium which scavenges metals from the solution (which would not necessarily apply if only flocculant/lime were used.
MMER also requires the pH in the range 6 to 9.5, otherwise outside this range the bioassay of the discharge will fail the 50% survival rate.
How can we neutralize a pregnant leach solution to discharge to river? The pregnant leach solution pond contains 3500m3 of solution containing 18 g/liter Fe and 5 g/liter Ni at a pH of 1.0
Can you suggest a design for simple plan to neutralize the PLS to allow discharge of water to river? Thanks