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Sulfide - three-dimensional electrode joint deal with the printed circuit board wastewater

Author: YouXiangYu
Tutor: ChaiLiYuan
School: Central South University
Course: Environmental Engineering
Keywords: printed circuit boards wastewater sulfide precipitation method three-dimensional electrode ·OH radicals electrocatalysis oxidation electrochemical regeneration
CLC: X703
Type: Master's thesis
Year: 2009
Downloads: 167
Quote: 2
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Abstract


With the development of printed circuit boards,the species and quantities of electroplating additives were increased,which resulted in a large amount of the PCB wastewater with the properties of many complexing agents,high COD and low biodegradability discharged.The combinations of these chemicals and heavy metal ions make the wastewater more difficult to treat.In this study,the novel technology of sulfuration and electrolysis processes using "strong alkaline sulfide - three-dimensional electrode" was proposed to treat the wastewater containing complexes of Cu-EDTA efficiently.Firstly, the heavy metal was removed with the upset of the coordination equilibrium. and then the organic matter was degraded with advanced oxidation processes （AOPs）.The conclusions are shown as follows:（1） Diagrams for the concentration of complex ions pc-pH,the ratio of four kinds of hydroxy complex ionsαn-pH in the Cu2+-H2O system were drawn respectively.The relationship between the equilibrium concentration of total copper ions and pH value was shown in Cu2+-H2O system.The diagram forαn-pH showed that each hydroxy complex ion existed in the system is dependent upon an optimized pH value.In the Cu2+-EDTA-S2--H2O system, curves for lg[Cu2+]and pH of the Cu2+-H2O system.（dissolution equilibrium）, the Cu2+-H2O system（coordination equilibrium）,the Cu2+-EDTA-H2O system, the Cu2+-S2--H2O system were drawn respectively.At the pH value range of 7 to 14,free copper ion in the Cu2+-S2--H2O system was lower than that in the Cu2+-EDTA-H2O system,which showed that the copper in the Cu2+-EDTA-H2O system could be removed by using sulfide precipitation method.In the system without EDTA,precipitate of Cu（OH）2 was formed at pH value range of 7 to 12.5.In the system with EDTA,complexing ion of copper and EDTA was formed,which showed that the simple neutralization precipitation can not remove copper from the Cu2+-EDTA-H2O system.（2） The sulfuration method at strong alkaline media was used to remove the heavy metal by upset the coordination equilibrium.Influence factors,including hydrolyzed time,sulfide precipitation time,pH value, dosage of sodium sulfide,temperature and PAM dosage were examined respectively through the single factor experiments and orthogonal design experiments.The process parameters were determined as the hydrolyzed time of 10 min,sulfide precipitation time of 30 min,pH value of 13.0,the mol ration of sulfur and copper of 1.2,temperature of 45℃,PAM dosage of 6 mg/L.Under the above optimal conditions,the removal rate of copper can be reached up to 99.37%.Rrange analysis indicated pH value is the first factor to be considered,and then hydrolyzed time,sulfide precipitation time,dosage of sodium sulfide in turn.（3） The electrolysis method of "three-dimensional electrode" was putford to degrade organic matter.The influence factors,including pH value, influent flow rate,temperature,electric conductivity,current intensity and electrolysis time were examined respectively through the single factor experiments and orthogonal design experiments.With the membrane,the removal efficiency of total organic carbon（TOC） was 96.40%when pH value range of 6.0-8.0,influent flow rate of 200mL/min,temperature of 25℃, electric conductivity range of 1.0 ms/cm to 1.5 ms/cm,current intensity range from 200mA to 300mA,and electrolysis time 1h were all practiced.The range analysis showed that the important order of relevant factors was:electric conductivity > current intensity > electrolysis time > temperature > pH value. Without the membrane,the conditions were almost the same,but due to the lower voltage,the current efficiency was higher.（4） EDTA was degraded by synergistic effect of two electro-catalytic oxidation methods with added tert-butyl alcohol as·OH radicals scavenger. The direct oxidation was that EDTA was adsorbed on the surface of particle electrode and graphite electrode,and then was oxidatively degraded under catalysis.The indirect oxidation was that organic matter was degraded by·OH radicals which come from water electrolysis.（5） The impregnation method was adopted to activate carbon modification.The effect of Mn（NO3）2,as an impregnating solution,was examined in the modified process.The catalytic activity of modified carbon has no change comparing with that of unmodified carbon.The failure of modification resulted from the leaking active component and the phenomenon that Mn2O3 crystals with catalytiv activity was not formed.XRD patterns illustrated that the main crystals in the modified carbon was Mn3O4.（6） The analyse of the infra-red spectrograms determined that the activated active carbon adsorption,σ-σ* feedback bond formed,so the chemical bonds was broken and EDTA was degraded into glycine.When the activated active carbon was used for many times,glycine molecule changed into association with the chemical bond of N-H on activite carbon.The association complex may be non-catalytic activity compound,which can hardly remove in the electrolysis process.Therefore,the activate carbon lost the activity.The method of "three-dimensional electrode" electrolysis was used to produce·OH radicals which can degrade the association complex individually.The influence factors,including reaction time,electric conductivity,current intensity,pH value and temperature were examined.The process parameters were determined as the electrolysis time of 1h, temperature of 25℃,electric conductivity of 1.39ms/cm,the current intensity range from 6 to 8.Under such conditions,the activity of the activated active carbon can be recovered and the removal efficiency of organic matter ia also be maintained at 90%.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization
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