Industrial Study On The Recycled Usage Of Wastewater From The Process Of Mn₃O₄Production By Oxidizing Metal Manganese Powder Method

Currently, in China, more than80%of Mn3O4is prepared by oxidizing method by using metal manganese powder suspension as raw material, which consumes5-20tons of water per ton of Mn3O4and produce large amount of wastewater. In the wastewater, the concentration of Mn2+and NH4+are about500mg·L-1and400mg-L-1respectively, which are all above the national wastewater discharge standards and require further treatment before discharging. A common solution is removing the Mn2+by chemical precipitation method and removing NH4+by the air blow off method. But this method can’t solve the environmental problems caused by the Mn3O4production wastewater absolutely. In order to address this problem, in this thesis, a novel technology including two main steps for the wastewater treatment was developed. Firstly, Mn2+was removed by chemical precipitation method; then, Ca2+and Mg2+were removed by ion exchange method. After these two steps, the recycled use of water can be realized. The main contents and conclusion are detailed as follows:The thermodynamic analysis on the Mn2+-Mg2+-NH4+-OH--H2O system shows that the manganese could be deeply purified when the pH of the system is up to10. The result of adsorption isotherm experiments demonstrates that the adsorption process can be fitted well to the Freundlich model, and the process is endothermic, which means higher temperature is conducive to the adsorption of Ca2+and Mg2+by D113resin.The optimal operation conditions confirmed by experiments are as follows:reaction time30min, the dosage of ammonia0.4%(V/V), the dosage of hydrogen peroxide0.1%(V/V). Under these experimental conditions, the concentration of Mn2+would reach0.035mg·L-1from450mg-L-1, resulting the removal ratio of manganese ion being99.99993%. The adsorption and desorption ratios for Ca2+and Mg2+ions were detected to be100%and99.06%respectively by dynamic adsorption and desorption experiments. And the flow rate could influence the resin capacity:the slower the liquid flow, the larger the resin adsorption capacity. The production experiment conducted in the laboratory shows that the products synthesized by using the abovementioned purified water can meet the quality standards.The optimum process operating parameters established through the Industrial experiment are:the dosage of ammonia0.4%(V/V), the dosage of hydrogen peroxide0.1%(V/V),agitation speed60r·min-1, reaction time60min. Through which, the concentration of Mn2+would drop to0.026mg·L-1from491.5mg·L-1, indicating that the removal ratio of manganese ion could reach99.99995%. A ion exchanger of1.5m in diameter and4m in depth was used for industrial experiments, which was filled with2t resin. When the liquid velocity is5.7m·h-1, the Ca2+and Mg2+can be thoroughly removed. The adsorption capacity of resin is tested to be around1208mmol·L-1before the concentration of Mg2+reaching up to0.5mg·L-1in the effluent, and the resin regeneration cycle is10days. The Industrial experiments also shows that the products produced with the water purified by the novel technology meet the quality standards.