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With the discharge limit of “electroplating pollutant discharge standard” more and more strict, now, the treatment of heavy metal wastewater has become the focus of major industrial attention. Now the often treated heavy metal wastewater complexed and free state, among which, complexed metal wastewater has strong toxicity, treatment is relatively difficult. And because of the low biochemistry of this kind of water quality, so now the main physical and chemical treatment, common treatment means is the use of collateral breaking agent, heavy metal capture agent and sodium sulfide and other chemical treatment.

Sodium sulfide has the effect of collateral breaking and sulfide precipitation of heavy metal pollutants, and low price, so the current industry is more using sodium sulfide to treat complex heavy metal wastewater. This paper mainly introduces the use of sodium sulfide and adding steps, the details are as follows.

In fact, the addition step of sodium sulfide is mainly determined according to the actual situation of the site, the following are a few steps for the use of conventional sewage treatment process.

1. Sodium sulfide is added at the back end of the regulating tank. Because sodium sulfide is a nature can not be used under acidic conditions, so it is necessary to add alkali before use, in order to prevent the production of toxic and harmful substances volatilization, but also to ensure effective treatment, with the complexed state and free state metal ion reaction to sulfide precipitation.

2. Add sodium sulfide into the reaction tank. If in the field debugging, the actual conditions, sodium sulfide can be added in the broken after (alkaline) reaction pool, because the complexation metal ion has been broken become free metal ions, so in the reaction pool after broken again add sodium sulfide treatment is more helpful to improve the treatment effect of metal pollutants.

3. Add sodium sulfide at the front end of the coagulation tank. Before the coagulation treatment, sodium sulfide is added to precipitate the metal ions. Because most of the metal ions have been settled, the subsequent coagulation treatment can further treat the residual metal ions, so that the water quality can be purified and the standard rate is higher。