The Relational Experimental Research Of Nace Membrane Distillation For The Treatment Of Heavy Metal Wastewater

Heavy metals are one of the most common industrial pollution emissions in the electroplating,mining and other industries,which seriously threaten human health and living environment.The current heavy metal wastewater purification process has the disadvantages of high energy consumption,serious secondary pollution,etc.How to improve the heavy metal wastewater treatment efficiency has been the focus of researchers at home and abroad.In order to efficiently purify heavy metal wastewater and recover precious metals in some wastewaters,NACE membrane distillation technology was used to conduct experiments on heavy metal wastewater treatment.First,the single factor experiments ontransmembrane volumeand the retention rate of metal ions were studied.With the aim of recovering precious metals,experiment group used orthogonal experiments to optimize operating parameters,and explored the best conditions for working conditions with the maximum transmembrane volume,and designed and built a pilot experiment platform for intermediate experiment certification on the basis of small experiment trials.Membrane fouling agents were screened.It provides a new idea for the treatm-ent of heavy metal wastewater,and also provides technical support for the industrial application of NACE membrane distillation technology.It has a practical significance.The main conclusions of this study are as follows:(1)The experiments explored the effects of metal ion valence,hot-side temperature,pH,concentration,and cold-side vacuum on the transmembrane volume andretention rate of metal ions of the NACE membrane evaporator.From the results of experiment,the higher the metal ion valence and concentration is,the greater the retention rate of metal ions is,and the higher the hot-side temperature and cold-side vacuum degree is,the higher the transmembrane volume is.(2)In order to optimize the conditions for precious metals recovery,Tag-uchi was designed and the results were analyzed.Theexperiment results show that when the metal concentration is 16%,the ion valence is +3,the vacuum degree is 0.094 MPa,pH is 7 and the temperature is 80 ?,the retention rate of metal ions has the best effectThe order of significance of the factors affected is:concentration>valence of metal ions>cold-side vacuum degree>pH>hot-side temperature.(3)A combination of Plackett-Burman and Box-Behnken experimental designs was used to screen and optimize the influencing factors to obtain the maximum transmembrane volume.The results show that the hot-side tempera-ture,cold side vacuum of the NACE membrane evaporator and pH are the main factors affecting the transmembrane volume.When the optimal conditio-ns are 78.09 ?,0.098 MPa,and 3.04,the 95%confidence interval of the maximum transmembrane volume model prediction is 12.89-14.19 L/(m2·h).(4)The pilot experiment platform was designed and the pilot research was conducted under the optimized Box-Behnken method.The results showthat the transmembrane volume in the pilot experiment was between 13.57 and 15.27 L/(m ·h),which was in good agreement with the range of the predicted values of the small pilot model.(5)Four cleaning agents were used to conduct cleaning experiments on the contaminated NACE membrane.The results show that 4%hydrochloric acid and citric acid have a good descaling effect.Compared with the price,citric acid is recommended as a descaling agent.