Study On Treatment Of Ammonia Wastewater From Electrolytic Manganese

In the recent decades, electrolytic manganese industry developed rapidly and promoted the local economic construction, simultaneously, brought serious environmental problems. Water pollution is the most severe which contains the harmful substances, such as manganese ions and ammonia, suspended solids, chromaticity and so on. At present, China’s electrolytic manganese enterprises do not form a complete set for the ammonia treatment, almost direct emissions it to river which would pose a serious threat to environment and human. It is very urgent to control ammonia pollution and adopt corresponding measures to dispose it for electrolytic manganese industry.This paper adopted electrochemical method and chemical precipitation method for treating ammonia in electrolytic manganese process wastewater and manganese residual leachate respectively. The conclusion is as follows:This paper studied electrochemical oxidation of ammonia with DSA anode, and discussed the influence factors. It was found that direct electro-oxidation of ammonia was not obvious, but indirect oxidation in presence of chloride ions played a major role for ammonia removal. In order to avoid the secondary pollution brought by adding chlorine ion, this paper designed the diaphragm electrolyzer for treating ammonia and Mn2+ in the wastewater, in which electro-deposition and electro-oxidation processes were used. The reactor was separated into two chambers by a fibrous membrane. The anode was Ti/Ru O2·Ir O2·Sn O2, and the cathode was stainless steel electrode. Factors affect the removal efficiency of ammonia nitrogen were studied, such as the mole ratios of nitrite and ammonia, voltages, initial p H value. As a result, up to 97.2% of total ammonia could be removed with an initial concentration of 120.2 mg·L-1. Moreover, the electro-catalytic properties and characteristics of ammonia oxidation on platinum electrode were observed from the cyclic voltammogram. Under the optimum experimental conditions, the concentration of ammonia nitrogen and manganese can meet the national discharge standards(15 mg/L, 2 mg/L).Magnesium ammonium phosphate crystallization could effectively remove ammonia from electrolytic manganese residual leachate. This paper investigated factors that influence ammonia removal, Mg Cl2·6H2O plus Na2HPO4·12H2O was the best precipitant combinations, the optimum p H was 8, optimum molar ratio of Mg2+:NH4+:PO43- was 1.2:1:1, the residual ammonia was lower than 15mg/L. The XRD, FTIR and SEM analysis indicated that the main composition of the precipitate was Mg NH4PO4 and unshaped coarse crystal. In order to reduce the treatment cost and recycle MAP, precipitation pyrolysis of MAP has been investigated in the present study. The XRD, FTIR analysis confirmed that magnesium sodium phosphate(Mg Na PO4) was obtained from magnesium ammonium phosphate pyrolysis process with mole ratio of OH-:NH4+ 1:1, temperature 80~100 ℃ and 3h. When using sodium phosphate magnesium for treatment of ammonia wastewater, NH4+ can replace Na+ of Mg Na PO4 to generate Mg NH4PO4 again, and thus the goal of sediment recycling was achieved.