Study On The Recovery Of Ammonium And Magnesium Resources From Electrolytic Manganese Wastewater

China is the country with the largest output of electrolytic manganese metal,accounting for 98%and 90%of the world's total respectively.However,a large amount of exhaust gas,waste water and waste residue are discharged during the production of electrolytic manganese metal.The high concentration of CO₂ contained in the exhaust gas will exacerbate the global warming effect.Wastewater and waste contain high concentrations of pollutants such as manganese,magnesium and ammonia that pose a significant environmental risk.In particular,a large amount of magnesium and ammonium ions contained in the electrolytic manganese wastewater cause tremendous pressure on the current efficiency caused by the production process of the electrolytic manganese,clogged pipes and the sewage treatment section.Therefore,the"Three wastes"is the urgent task of the entire electrolytic manganese industry needs to be addressed.In this paper,a manganese dioxide plant in Guangxi by manganese removal pretreatment of wastewater,the use of ammonium phosphate precipitation and carbon dioxide two methods of carbon dioxide were recovered electrolytic manganese wastewater ammonium,resources.By investigating the effect of reaction time,pH,temperature,and phosphorus source on the recoveries of ammonium,magnesium and calcium,the optimum technological conditions for the recovery of ammonium and magnesium in electrolytic manganese wastewater by ammonium phosphate precipitation were determined.The results showed that when the initial NH₄⁺,Mg²⁺and Ca²⁺concentrations were 875mg·L^-1,1200 mg·L^-1,560 mg·L^-1,the reaction time was 30 min,the pH value was 9.0,the reaction temperature was 25?,Under the condition of N=1.1:1,the recoveries of ammonium,magnesium and calcium reached 80%,99.35%and 94.08%respectively,and the residual phosphorus content was 20.34 mg·L^-1.At the same time,the mechanism of crystallization reaction of magnesium ammonium phosphate?MAP?was studied.The results show that there are crystal transitions of magnesium phosphate,magnesium hydrogen phosphate and magnesium ammonium phosphate in the process of MAP formation.There are also NH₄⁺and Mg₃?PO₄?₂?s?,The formation of Mg₃?PO₄?₂?s?in the crystallization reaction of MAP,the formation of MgHPO₄ in the system and the formation of MAP crystals together with NH₄⁺into the Mg₃?PO₄?₂?s?crystal phase.By investigating the influence of reaction temperature,pH,temperature,stirring rate and carbon dioxide concentration on the recoveries of ammonium,magnesium and calcium,the optimal conditions for the recovery of ammonium and magnesium in the electrolytic manganese wastewater by CO₂ carbonization were determined.The results showed that in the initial ammonium,Under conditions of magnesium concentration of875 mg·L^-1,1200 mg·L^-1,560 mg·L^-1L,reaction time of 240 min,reaction temperature of 45?,pH value of 9.2,carbon dioxide volume concentration of 15%and stirring speed of 600 rpm,The recoveries of NH₄⁺,Mg²⁺and Ca²⁺reached 80.71%,97.58%and99.68%,respectively.In order to study the reaction mechanism of recovery of magnesium from waste water of manganese dioxide by CO₂ carbonization,the reaction process was studied by first-order reaction kinetics and Avrami-Erofeev isothermal crystallization kinetics model.The adsorption kinetics of ammonia nitrogen was also studied.The results showed that the reaction system for the formation of basic magnesium carbonate by magnesium carbide in the manganese dioxide wastewater was in accordance with the first order reaction kinetics.The reaction rate constants were0.0087,0.02911 and 0.04092 min^-1 at 25,35 and 45?,respectively The activation energy is 61.40 kJ·mol^-1.The basic magnesium carbonate belongs to the one-dimensional crystallization process of the rod-shaped crystals.The apparent activation energy of the nucleation phase is-63.69 kJ·mol^-1and the apparent activation energy of the crystal growth phase is 32.04 kJ·mol^-1;the adsorption process of ammonia nitrogen conforms to quasi-second order reaction kinetics,and the apparent activation energy is-55.56 kJ·mol^-1.