In this example a processing plant was spending in excess of $300K/yr on chemical antiscalant for their process water, yet were still experiencing scaling in the process water lines. The program was maintained at a single dose rate year round, set at a upper limit based on allowable cost. The main form of scale they were aiming to control was Gypsum, which came out of solution once the critical level of sulphate and calcium was reached in the process water, with the sulphates coming from sulphide oxidation in the tailings dam, and the calcium from lime addition for pH control. There were no adequate records of water quality, so a fortnightly monitoring program of water samples was implemented and scale probes were put in place. The mine site was located in a tropical region, with massive input of fresh water in the wet season and evaporation in the dry season. Using the water samples it was determined that minimal antiscalant was required nine months of the year, the previous dose rate for 2 months and double the previous dose rate for the last month of the dry season. The net effect of the modified program was no detectable process water system scale, and chemical program cost of $80K/yr ($280K/yr saving).
Another effect noticed on the plant was lower selectivity (and hence recovery at target grade) for the zinc flotation circuit. Of note was the addition of copper sulphate and lime prior to the zinc collector (SIBX in this case). It is hypothesised that this was due to scale forming on the active surface of the liberated zinc mineral particles due to the lime addition causing gypsum to form on the surface, but testing to prove this was not conducted, though it was noted that the Zinc grade recovery was better when lime addition was lower during this period of concern.
As you can see from the above example, had the processing personnel received proper support they would have achieved significant savings (the program had been in place for four years, giving a potential indication of a program saving of $880K). An initial audit of their water systems and training of site personnel on how to correctly audit the water chemistry would have cost less than $20K, with perhaps $10K/ yr for ongoing support. That is a fantastic return on investment. Unfortunately the antiscalant supplier at the time did not provide the required technical support. An independent audit costing around $1000-2000 would have identified the issues with the program, and could have designed a solution and trained site personnel to monitor and adjust.
Another effect noticed on the plant was lower selectivity (and hence recovery at target grade) for the zinc flotation circuit. Of note was the addition of copper sulphate and lime prior to the zinc collector (SIBX in this case). It is hypothesised that this was due to scale forming on the active surface of the liberated zinc mineral particles due to the lime addition causing gypsum to form on the surface, but testing to prove this was not conducted, though it was noted that the Zinc grade recovery was better when lime addition was lower during this period of concern.
As you can see from the above example, had the processing personnel received proper support they would have achieved significant savings (the program had been in place for four years, giving a potential indication of a program saving of $880K). An initial audit of their water systems and training of site personnel on how to correctly audit the water chemistry would have cost less than $20K, with perhaps $10K/ yr for ongoing support. That is a fantastic return on investment. Unfortunately the antiscalant supplier at the time did not provide the required technical support. An independent audit costing around $1000-2000 would have identified the issues with the program, and could have designed a solution and trained site personnel to monitor and adjust.
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