Study On Flocculation Of Chromium In Wastewater By Pulse Alternating Current And Adsorption Mechanism

The production process of leather making,electroplating and other industries produced large amounts of wastewater containing chromium bring about serious enronmental pollution problem which were harmful to our food and drinking water.There are conventional methods in the treatment of wastewater containing chromium,such as direct current electrolysis and chemical reduction method.These methods have the defects of high-cost and low removal efficiency.The electrocoagulation possess has many advantages of the treatment efficiency,cost and operability.We have designed the double iron electrodes technique of PAC base on electrochemical oxidation reduction and adsorption principle.The double iron electrodes technique of pulse alternating current?PAC?floculation was applied to treat wastewater containing chromium???,the parameters of affecting the removal rate of chromium in wastewater were studied with the help of the developed new electrochemical reactors.The concentration of chromium??,??in the effluent was measured by UV Spectrophotometry.The simulated wastewater contained 100mg?dm^-3Cr???and NaCl as conductive salt and the pH value was adjusted to 4 with ammonia or sulfuric acid.Under the conditions of room temperature?20-25??,applying the PAC density of 40?A?g_Fe^–1,at the flow rate of 2 dm³?min^-1,the concentration of chromium???in the wastewater was reduced to 0.090 mg?dm^-3after passing through four-series reactors,which was lower than 0.5 mg?dm^-3from GB8978-1996.When the pH value of effluent was adjusted to 8 and flocculation was conducted,the concentration of Cr???can be reduced to 1.39 mg?dm^-3,the total chromium content(about 1.48 mg?dm^-3)of the effluent is close to national wastewater discharge standard 1.5 mg?dm^-3from GB8978-1996.The double iron electrodes technique of PAC floculation was applied to treat wastewater containing chromium,in this process,the adsorption process of floc was existed,In this paper,the adsorption mechanism was characterized:?1?Compared with the iron sol produced by chemical method,the iron sol surface structure is more complex which is produced by PAC.?2?EDS energy spectrum analysis showed that Chromium adsorbed on iron sol which produced by chemical reduction method less than PAC flocculation.?3?XRD analysis showed that iron sol?Fe?OH?₃?have different diffraction peak between adsorption and non adsorption.Fe???forms macromolecule ion complex by hydration,complexation and adsorption,then the Cr???in waste water is trapped and formed an electric agglomerate.?4?Adsorption of Cr???with different amounts of iron sol show that the adsorption of iron sol on Cr???follows the adsorption of Langmuir monolayer,dynamic equilibrium can be established between adsorption and desorption.The removal rate of chromium ions in wastewater via PAC floculation was higher than that of traditional electrochemical method and chemical reduction method.The removal rate of chromium???reached 99.91%and the removal rate of total chromium was 98.13%via PAC floculation.Applying the novel double iron electrodes technique of PAC to floculate wastewater containing chromium,the removal of chromium ion in wastewater was far more efficient than the traditional electrochemical method and chemical reduction method.It implies that the PAC floculation was used to reduce the concentration polarization and electrode passivation,at the same time,the resulting gel can help to adsorb heavy metal ion which improve the current efficiency.The low cost treatment technique will produce significant economic and social benefit.