The redox potential is controlled at Electroplating wastewater treatment equipment Application in.
Electroplating wastewater contains cyanide and various heavy metal ions with high toxicity and high pollution. If the discharge is not treated, it will certainly pose a serious threat to the life, health and ecological environment of human beings and other animals. The purpose of this paper is to control the redox potential, fine treat hexavalent chromium and cyanide ions, and reduce toxicity. This paper focuses on the analysis of the principle, application methods and control points of the redox reaction of hexavalent chromium ion and cyanide ion, which improves the treatment efficiency of related pollutants.
Direct discharge of electroplating wastewater without electroplating wastewater treatment equipment is very harmful, especially hexavalent chromium ion and cyanide are toxic to relevant water bodies, animals and plants in water bodies. Therefore, it is of far-reaching significance to deeply analyze and study the pollution components in chromium containing wastewater and cyanide containing wastewater, treat hexavalent chromium and cyanide, and complete the harmless process. In the actual treatment process, one of the main methods is to control the oxidation-reduction potential, and input oxidant and reducing agent according to the actual situation of water quality, so as to ensure that the chromium containing wastewater meets the specific requirements of Table 2 of the electroplating pollutant discharge standard (GB21900-2008) for on-site discharge outlets. In addition, after the removal of characteristic pollutants from chromium containing wastewater and cyanide containing wastewater, the wastewater quality is single, and the treated tail water can be recycled, which can effectively save the recovery of water resources.
Important reaction of electroplating wastewater treatment equipment application.
The main characteristic pollutant indicators of chromium containing wastewater and cyanide containing wastewater are hexavalent chromium and cyanide, which not only pollute themselves, but also are not conducive to the treatment of other heavy metals. At present, the mature treatment method is the potential method of controlling oxidation and reduction. Hexavalent chromium and cyanide are reduced by NaHSO3 and oxidized by NaClO respectively, and the corresponding redox reaction modes are (1), (2) and (3). In formula (1), under strong acid conditions, hexavalent chromium is reduced to trivalent in the process of oxidation and reduction; In Formula (2), cyanide is converted to sodium cyanate under strong alkaline conditions, and redox reaction continues under strong alkaline conditions. For example, Formula (3) is oxidized to CO2 and N2 in the redox process, and Formula (2) and (3) respectively correspond to the primary and secondary oxidation of cyanide in the redox process. The fourth is to select control points.
1 Wastewater containing chromium.
During the treatment of chromium containing wastewater, hexavalent chromium has the highest redox potential, and the redox control point can be determined according to the titration curve. NaHSO3 is used as reducing agent in actual production and operation. According to pH value, the redox potential change of NaHSO3 reducing agent is shown in Figure 1. When the pH value is between 2 and 3, the redox potential difference is between 180 and 280 mV, which is consistent with the analysis results of the above types (7) and (8), that is, when the pH value is 2.5, the corresponding redox potential is 250 mV.
Second, cyanide containing wastewater.
The redox control point can also be determined according to the drip curve, as shown in Figure 2. When the potential near the point is prominent, it can be used as a reference control point. In the actual production and application process, when the pH value is 11, the corresponding redox control potential is above 350mV.
Third, electroplating wastewater is complex.
The above two cases are electroplating wastewater, including the main characteristic pollutants, but there is ground wastewater in the actual production treatment and operation process, including CN - and Cr2O2-7, including other electric pairs. According to the theoretical reference, the potential deviation is obvious and should be based on the actual change. The quantitative procedure is as follows.
1) Place the sensor in the raw water of complex electroplating wastewater, measure the pH value and initial redox potential 2) In operation, under alkaline conditions, when the pH value is adjusted to 10-11, put in the oxidant sodium hypochlorite agent, maintain the redox potential above 350mV, fully stir the reaction, complete the primary and secondary cyanide removal technologies 3) When adjusting the pH value of the effluent after cyanide removal to 2.5, Put in the reducing agent NaHSO3 solution to reduce Cr2O2-7, maintain the redox potential below 250mV, and complete the chromium breaking technology after fully stirring the reaction 4) After the cyanide and chromium breaking, the corresponding copper and chromium ions are removed from the wastewater through chemical precipitation. 5) In actual operation, always pay attention to the change of redox potential and pH value, and adjust the input of oxidant, reducing agent, liquid alkali and hydrochloric acid in time to ensure the complete removal of cyanide and hexavalent chromium.
By analyzing the operation of treatment equipment for cyanide containing wastewater, chromium containing wastewater and complex electroplating wastewater, subdivide and control the parameter values of pH value and redox potential, effectively remove CN - and Cr2O2-7, reduce the toxicity of electroplating wastewater, effectively ensure the removal of heavy metal ions from cyanide and chromium breaking electroplating wastewater by chemical precipitation, and correctly control the redox potential parameters, Reduce the concentration of pollutants to a large extent, improve the use efficiency of chemicals, reduce costs, and realize the combined benefits of social benefits, environmental benefits and economic benefits.
