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Hi Guys,
We have been experiencing an interesting phenomenon and am wondering if anyone with a stronger hydromet background could explain why.
We have been getting high levels of arsenic in our gravity ILR bullion. We have been using hydrogen peroxide as an oxygen source in our leach at pretty typical intensive leaching conditions.
20,000 ppm NaCN
pH ~12 with NaOH
Peroxide addition to maintain DO from 16-22 mg/L
Our pregnant solution is almost totally clear, ICP scans on the solution show minimal arsenic but when we smelt the sludge we still sometimes have 5%+ As showing up in our bars.
We have done a few batch trials using SeproLeach as an alternative oxygen source (I believe this is the same chemical as "LeachAid") and have noticed significantly lower Arsenic grades in the first pour we did without peroxide.
Is it possible that peroxide somehow causes arsenic precipitation into our EW sludge but a chemical oxidant would not cause this same phenomenon?
If this is the case, it will definitely help our case in switching from peroxide to SeproLeach but if I had a scientific explanation as to why this is happening it would be easier to convince my boss.
Thanks!