Heavy metal wastewater mainly comes from the wastewater discharged from mining, smelting, electrolysis, electroplating, pesticide, medicine, paint, pigment and other enterprises.
The types, contents and existing forms of heavy metals in wastewater vary with different production enterprises.
Because heavy metals cannot decompose and destroy, they can only transfer their place of existence and their physical and chemical forms.
For example, after chemical precipitation treatment, heavy metals in wastewater are precipitated from dissolved ion form to insoluble platform and transferred from water to sludge.
After ion exchange treatment, heavy metal ions in wastewater were transferred to ion exchange resin, and then from ion exchange resin to regenerated waste liquid.
Therefore, the principle of heavy metal wastewater treatment is: first, the most fundamental is to reform the production process.
Use no or less toxic heavy metals;
Secondly, reasonable technological process, scientific management and operation are adopted to reduce the amount of heavy metals and the amount of waste water lost along with it, and the amount of effluent discharged outside is minimized.
Heavy metal wastewater should be treated at the site where it is produced and mixed with other wastewater so as not to complicate the treatment.
Moreover, it should not be discharged directly into urban sewers without treatment to avoid expanding heavy metal pollution.
The treatment of heavy metal wastewater can be divided into two types.
First, the heavy metal dissolved in the wastewater is transformed into insoluble metal compounds or elements, which are removed from the wastewater by precipitation and buoyancy.
The application methods include neutralization precipitation method, sulfide precipitation method, floating separation method, electrolytic precipitation (or floating) method, diaphragm electrolysis method, etc.
Second, the heavy metals in wastewater can be concentrated and separated without changing their chemical morphology. The application methods include reverse osmosis, electrodialysis, evaporation and ion exchange.
These methods should be used separately or in combination according to the water quality and water quantity of wastewater.