Study On Resource Utilization And Treatment Of Alkaline Etching Waste Liquor

There are high concentrations of Cu²⁺,Cl^-and NH₄⁺in alkaline etching waste liquor,which also contains a lot of complex components such as ammonia and chlorides.If alkaline etching waste liquor can not be effectively disposed,it will easily lead to serious human ecological pollution.Therefore,the alkaline etching waste liquor must be utilized and disposed effectively.First of all,two-step liquid-phase reduction was used to recover copper from alkaline etching waste liquor.Cuprous oxide particle was produced when glucose was used in the prereduction process under alkaline conditions,then thiourea dioxide was used as a reducing agent and polyvinylpyrrolidine was used as a dispersant,so cuprous oxide was reduced to single copper.Single factor experiments were conducted to investigate the effects of concentration ratio of thiourea dioxide and copper ion,glucose concentration,reaction temperature,reaction time and pH on the copper recovery.The results showed that when the concentration ratio of thiourea dioxide and copper ion was 1.25:1,the glucose concentration was 1.25 mol/L,the reaction time was 10 min,the reaction temperature was 70°C and the pH was 10,the copper concentration decreased from 112 g/L to 3.02 g/L,and the copper recovery was 97.3%.According to the results of single factor experiments,the recovery effect of copper mainly depended on the concentration ratio of thiourea dioxide and copper ions,reaction temperature and pH.Response surface methodology was used to optimize the key parameters.The copper recovery rate?%?was used as the response value,and Box-Behnken was used for the three-factor and three-level center combination experiment.According to the quadratic regression fitting,the regression equation was obtained.Through variance analysis,the P value of the model was 0.0001,P<0.05,the model was significant.The coefficient of determination was 0.9916,indicating that the regression equation can describe the actual process of copper recovery well and can be used to replace the experimental process for analysis and prediction.The optimal experimental conditions were determined to be the concentration ratio of thiourea dioxide and copper ion of 1.46:1,reaction temperature of72°C and pH of 9.7.Under these condition,the average copper recovery rate was 98.68%,the urea concentration was 6.97 g/L and the ammonia nitrogen concentration was 26.7 g/L.The structure,morphology and particle size of obtained products were characterized by X-ray diffractometry,scanning electron microscopy,infrared absorption spectroscopy and laser nanometer particle sizer.The product was flaky single copper powder with high purity and particle size in the range of 400-600 nm.Secondly,the reuse of tail fluid was discussed and analyzed.The copper in the tail fluid was recovered by micro-electrolysis and the results showed that treating 1 L alkaline etching waste liquor can save 80 g thiourea dioxide by reusing tail water.After 6 times of reuse,the copper recovery rate reached 99.4%and no significant change after continued reuse.The concentration of urea in the tail fluid increased significantly,reaching 10.3 g/L.The ammonia nitrogen concentration did not change significantly.The products that were reused for 6 times were all copper powders,and basically had a block structure.The less reuse times,the better dispersion of copper powder,the more uniform the surface distribution,and the smaller the particle size.Then,the tail liquid was recovered by micro-electrolysis and chemical precipitation.Micro-electrolysis was used to recover the copper in the tail fluid.The results showed that when iron powder dosage was 4%,reaction time was 90 min,rotation speed was 150 r/min and pH was 2.6,the effluent copper concentration decreased from 1480 mg/L to 41 mg/L,and the copper recovery was 97.2%.The copper ion concentration was reduced to 27 mg/L after filtration,and the corresponding copper removal rate increased to 98.2%.The chemical precipitation method was used to recover the ammonia nitrogen in the tail fluid.The optimal reaction conditions were determined to be pH of 10,the reaction time of 25 min,n(Mg²⁺):n?NH₄⁺?:n(PO₄^3-)=1.8:1:1.8.Under these condition,the average ammonia nitrogen remaining in the solution was 3.29 g/L and removal rate was 87.65%.The urea concentration decreased from 6.97 g/L to 3.09 g/L.The precipitates formed by the reaction were mainly magnesium ammonium phosphate crystals with a rhombic structure,high purity and uniform distribution.Finally,electrochemical method was used to remove ammonia nitrogen.The results showed that when the reaction time was 270 min,the initial pH of the solution was 11,the plate spacing was 2 cm,the current density was 60 mA/cm² and the NaCl dosage was 3 g,the concentration of ammonia nitrogen dropped to 0.473 g/L,and removal rate was about 82.86%.The concentration of copper ions decreased from 27 mg/L to 0.48 mg/L,and the removal rate reached 98.2%.When the electrolysis time was 180 min,the urea concentration decreased from 3.09 g/L to 0.9 g/L,and the total removal rate was 70.87%.As the electrolysis times continued,there was no significant change in the urea concentration.