The presence of sulphate, bicarbonate and orthophosphate can change the type of solid present in systems containing cupric ion or cupric hydroxide solids. In some cases, a short-term reduction in copper solubility is realized, but over longer periods of time formation of basic cupric sulphate (brochantite) and even cupric phosphate can ultimately prevent the formation of very insoluble tenorite or malachite phases. To the extent that this occurs, the presence of sulphate and phosphate in water can increase copper solubility over much longer time periods. The relative effect can depend on the anion concentration and the rate of solids precipitation. Low levels of sulphate tend to hasten the transition from cupric hydroxide to tenorite, whereas higher levels of sulphate can interfere with that transition. These possible effects should be considered when attempting to reduce copper corrosion by-product release from consumer plumbing and similar transitions are likely important for other plumbing materials such as zinc, iron and lead.

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