Importance

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Abstract

A two-step chemical precipitation process involving hydroxide precipitation and sulfide precipitation combined with 'field separation ' technology such as magnetic separation, dissolved air flotation, vortex separation, or expanded plastics flotation, effectively removes chelated and non-chelated heavy metal precipitates and other fine particles from water. In the first-step, the non-chelated heavy metals are precipitated as hydroxides and removed from the water by a conventional liquid/solids separator such as an inclined plate clarifier to remove a large percentage of the dissolved heavy metals. The cleaned water is then treated in a second precipitation step to remove the residual heavy metals to meet discharge limits. In the second precipitation step, any metal precipitant more effective than hydroxide for metal precipitation can be used. The invention improves metal removal, lowers cost because fewer chemicals are used, produces less sludge, and reduces the discharge of toxic metals and metal precipitants to the environment. Magnetic separation is preferred for the separation of particles precipitated in the second stage. Similar methods can be employed for separation of other particulates from water. Particulates can also be removed by causing them to adhere to particles of expanded plastic, forming a floc lighter than water, so that the floc can be removed by flotation.

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First Claim