Study On The Synthetical Treatment Of Cr(Ⅳ)-containing Wastewater Produced By Formed-foil Industry

Treating Cr(Ⅵ)-containing wastewater is an important task with practical value. On the basis of surveying Cr(Ⅵ)-containing wastewater controlling approaches inside and outside country, and takeing a formed-foil factory wastewater as an example, Cr(Ⅵ)-containing wastewater treated by organic compound MK reduction and photo-catalytic deoxidization was studied systemically in this paper. In the study of treating high concentration(17000mg/L) Cr(Ⅵ)-containing wastewater by organic MK, factors affection reduction reaction were studied in details, such as reductant amount, pH value, time and temperature of reaction, etc. The optimization were determined to be: amount of MK: 10g/L; temperature: 98℃, pH value: 1.0, time of reaction: 10min. After deposition process, pure Cr(OH)3 can be reclaimed.The removal rate of Cr(Ⅵ) can reach the standard of charging. Aiming at the low concentration cleaning liquor and rudimental Cr(Ⅵ) solution, the photocatalytic deduction was adopted. Factors affecting photocatalytic deduction reaction were studied in a L16(45) orthogonal experiments, such as catalyst amount and varieties, pH value, intensity and time of light irradiation, etc. The affecting factors priority was introduced: catalyst varieties→pH value→intensity of light irradiation→time of light irradiation→catalyst amount.In order to analyze the cause of the affecting factors, adsorption of Cr(Ⅵ) on TiO2 decreased with the increase of the suspension pH. The largest Cr(Ⅵ) adsorption appeared when its initial concentration was about 15mg/L. The existence of H2PO4－ anion and acetic acid decrease the adsorption efficiency of Cr(Ⅵ),and formic acid promoted its adsorption efficiency. Other organic molecules had noninterference catalytic reduction of Cr(Ⅵ) on TiO2. H2PO4－ anion had inhibition on Cr(Ⅵ) reduction. Different organic compounds had different influences on Cr(Ⅵ) reduction because of their different electrical properties. Under the sunlight irradiation , Cr(Ⅵ) reduction was also observed on TiO2 photocatalyst. After separation of the catalyst, chromium was removed and detoxified from the waste water by adjusting the pH of the system. TiO2 photocatalyst was reactivated and reused after it was washed in acidic medium.The kinetics of phhotocatalytic deduction reaction for Cr(Ⅵ) solution was studied in catalyst suspension phase, the results showed that the reaction was first-order and the velocity of reaction was coincident with multiphase catalytic kinetic equation: Langmuir-Hinshelwood equation.