Heavy metal precipitation

In order to comply with the guidelines, heavy metals are typically neutralized by precipitating them out and separating them off from the wastewater using sodium hydroxide or milk of lime to turn them into poorly soluble hydroxides. However, these methods often fail because so-called complexing agents also tend to be present in the wastewater, which impairs or even completely prevents hydroxide precipitation. When this is the case, it is no longer possible to stay within the heavy metal limits.

Trimercaptotriazine (trisodium salt 15%) reacts with heavy metals such as lead, cadmium, copper, nickel, mercury, and silver to form highly stable, near-insoluble heavy metal-TMT compounds. Adding even small amounts can achieve good results even in cases where hydroxide precipitation has little or no effect at all. Typically, trimercaptotriazine is used in the neutral to slightly alkaline pH range. It forms a solid that can be easily separated off.

Trimercaptotriazine is being used successfully in more than a hundred wastewater treatment plants around the world due to its favourable toxicological and ecological properties as well as its high handling safety.

In addition to its proven use in wastewater treatment plants, it can also be added to the alkaline washers of incinerators to reduce mercury emission in the scrubbed gas. In the washer, the mercury becomes bound as a Hg-TMT compound and thus prevents its reduction to highly volatile, metallic Hg.

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