Views: 296 Author: nanombr Publish Time: 2018-11-27 Origin: Site
Heavy metals can accumulate in soil and can’t be degraded by microorganisms, but can only transfer their location and change their physical and chemical forms. The common treatment methods of heavy metal industrial wastewater are hydroxide precipitation, reduction, ion exchange, iron oxidation and electrolysis. Let's take a look at them.
Hydroxide precipitation method
Adding alkaline precipitators (such as lime milk, sodium carbonate, etc.) to heavy metal wastewater, the metal ions react with hydroxyl groups to form insoluble metal hydroxides precipitation, which can be separated.
Reduction method
Adding reductant to wastewater can reduce metal ions to metal or low-cost metal ions, and then adding lime to make them become metal hydroxide precipitation. This method can be used to recover copper, mercury and other metal ions, and is often used in the treatment of chromium-containing wastewater. Chromium-containing wastewater mainly exists in the form of complex ions of hexavalent chromium, which can be reduced to trivalent chromium and then removed by adding lime to form chromium hydroxide precipitation.
According to the different reducing agents, it can be divided into ferrous sulfate method, sodium bisulfite method, sulfur dioxide method, iron powder or iron filings method, etc.
Ion exchange method
The exchange group of ion exchanger is used to exchange with metal ions in wastewater. The metal ions are replaced on the exchanger and removed.
Ferrite method
The oxides consisting of iron ions, oxygen ions and other metal ions are ferromagnetic semiconductors. The treatment of heavy metal wastewater by ferrite process is based on the principle of ferrite manufacturing. The bivalent or trivalent metal ions in wastewater are filled into the lattice of ferrite spinel by ferrite reaction. Thus, precipitation separation can be obtained. A dark green hydroxide is formed when alkali is added to the solution where divalent metal ions coexist. When heated to 50-70℃ and oxidized by air, hydroxides dehydrate and finally form brown-black magnetic spinel ferrite precipitation.
Electrolytic process
Aluminum (or iron) was used as soluble anode, stainless steel or aluminum or iron as cathode, and wastewater was electrolyzed under DC electric field. After electrification, the anode metal (aluminum or iron) discharges into metal ions and dissolves into the wastewater to form aluminum hydroxide or ferric hydroxide colloid. At the same time, the heavy metal ions in the wastewater combine with the OH - produced by the cathode to form metal hydroxides, which are adsorbed on the anode to form hydroxide colloid and precipitated together. In addition, the metal ions in the wastewater can also directly obtain electrons on the cathode, which can be reduced to metal deposited on the cathode.
