Plastic Plating-treatment Process Of Hexavalent Chromium Wastewater By Electroplating

Plastic plating-treatment process of hexavalent Chromium Wastewater by Electroplating.
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The research on the treatment of hexavalent chromium electroplating wastewater is very active in our country. The basic line is to reduce hexavalent chromium to trivalent chromium with low toxicity, and then remove it by chemical precipitation. Its methods include chemical reduction, electrolytic reduction condensation, etc.; second, there are many research reports on resource recovery routes, such as ion exchange, activated carbon adsorption, reverse osmosis and so on. Among them, chemical reduction method, ion exchange method and electrolytic reduction method are more common.
Chemical reduction method.
The chemical reduction treatment of wastewater containing hexavalent chromium mainly includes chemical reduction method, ferrite method, iron filings iron powder reduction method and so on. The basic principle is that under acidic conditions, hexavalent chromium is reduced to trivalent chromium by chemical reducing agent, and then precipitated by alkali to form chromium hydroxide precipitation.
Basic process parameters of chemical reduction method.
The hexavalent chromium in electroplating wastewater mainly exists in the form of CrO,-1 and Cr207-2. With the difference of pH in electroplating wastewater, there is a conversion balance between the two forms: 2Cr0 ~ (2 -) + 2H + v ~ (2). Cr2Or2-+ H2OCr2072-+ 20H-- 2C r20mae2murine 2H20 shows that hexavalent chromium exists mainly in the form of Cr20 production under acidic conditions, while I9 exists in CI 0,2-form under alkaline conditions. However, the concentration of Cre+ in electroplating chromium-containing rinsing wastewater is generally within the range of 20 100rng/1 ", and the wastewater is generally above pH5, mostly in the form of Cr0,2.
The reduction of hexavalent chromium reacts quickly under acidic conditions, generally requiring pH < 4 and pH 2.5-3. The commonly used reducing agents are: sodium pyrosulfite, sodium sulfite, sodium bisulfite, sodium disulfite, sodium thiosulfate, ferrous sulfate, sulfur dioxide, hydration trap, iron filings iron powder and so on. The reduction reaction formula of chromic acid and the theoretical amount of reducing agent.
The Gr3+ after reduction is Cr (OH): the best pH of precipitation is 7-9, which is generally controlled in pH8, so the waste water after chromium reduction should be neutralized. The commonly used neutralizers are NaOH and lime. Some small enterprises neutralize wastes such as fly ash and calcium carbide paste.
When choosing chemical reduction and precipitation methods and reducing agents and precipitators for chromium-containing wastewater, not only the reduction and removal efficiency of chromium should be considered, but also the source and cost of agents should be considered. At the same time, the possibility of disposal and utilization of precipitated sludge should also be considered.