Electrochemical Stripping Of Cotton Fabrics Dyed With Reactive Dye In Water And Wastewater

In recent years,the recycle and reuse of waste textiles has been attracted more and more attention.The waste textiles could be made into nanocellulose or fermented into ethanol and methane through hydrolysis by cellulase.The dye on the surface of waste textiles can hinder the hydrolysis of cellulase.Thus,it is important to strip dye from waste textiles for improving the added value and promoting the reuse of waste textiles.Oxidants(OH,H2O2,hypochlorite,etc.)generated by electrochemical process have the ability to bleach pulp,textiles and indigo denim.Once the electrochemical method was employed for stripping of dyed cotton fabrics,the stripping of dyed cotton fabrics and the treatment of stripping effluent could occur simultaneously under the attack of oxidants generated in situ.In this study,Reactive Black 5,Reactive Red X-3B and Reactive Brilliant Blue KN-R were selected as dyes to be stripped from the surface of dyed cotton fabrics,water and simulated wastewater(pyridine,quinoline,phenol,Reactive Black 5,Reactive Red X-3B and Reactive Brilliant Blue KN-R solution)was adopted as stripping solutions.Active electrode and non-active electrode(?-PbO2 electrode)were separately used as anodes.Firstly,the parameters affecting the stripping performance of cotton fabrics were investigated using water as stripping solution.The possible electrochemical stripping mechanism of dyed cotton fabrics was proposed by analyzing the effluent during stripping.Then,the effect of pollutant existing in water on the stripping performance was investigated.The variation of pollutants and color removal of dye in water was determined.The competitive relationships between the stripping of dye from the dyed cotton fabrics and electrochemical oxidation of pollutant in water were explored.The effect of electrochemical stripping on the characteristics of un-stripped and stripped cotton fabrics was analyzed by Fourier transform infrared(FTIR)spectrometer.Finally,waste cotton fabrics were electrochemically stripped to investigate the feasibility for future practical application.The main results were as follows:(1)Reactive Black 5 dyed cotton fabrics with 1%(omf)was electrochemically stripped with NaCl in water.Reactive Black 5 dye could be easily stripped from dyed cotton fabrics through the cleavage of chromophoric group(-N=N-)under the attack of active chlorines and hydroxyl radicals(OH)generated in situ on the Ti/TiO2-RuO2-IrO2 anode.The stripping percent of the cotton fabrics in water and pyridine solution were maintained in the range of 98.4%to 98.9%.Whereas,phenol existing in water slowed the stripping rate.The stripping performance of the inner layer was superior to that of the outer layer.The result of FTIR analysis and weight loss of stripped cotton fabrics showed that the effect of electrochemical process and the existence of pollutant in water on the stripped cotton fabrics could be negligible.Electrochemical oxidation could also successfully strip various dyes from waste knitted cotton fabrics in the investigated stripping solutions.Promising stripping percent of Reactive Black 5,Reactive Red X-3B and Reactive Brilliant Blue KN-R dyed cotton fabrics with 6%(omf)color depth could be obtained on Ti/TiO2-RuO2-IrO2,Ti/TiO2-Ta2O5-IrO2 and Ti/TiO2-RuO2-IrO2-SnO2 anodes.The stripping percent and the whiteness index of stripped cotton fabrics were above 98.2%and 70,respectively.The competition between electrochemical oxidation of pyridine,quinoline and phenol in water and stripping of dyed cotton fabrics followed the order(from strong to weak):phenol>quinolinepyridine.(2).The stripping percents of dyed cotton fabrics on ?-PbO2 anode in water,pyridine,quinoline and phenol solutions containing NaCl electrolyte after 10 min of stripping were over 95.0%,indicating that OH and active chlorine generated on ?-PbO2 anode were mainly used for stripping dye from dyed cotton fabrics.The FTIR analysis results showed that the effect of electrochemical stripping and pollutants existing in water on the quality of stripped cotton fabrics could be negligible.Electrochemical oxidation could also strip various dyes from waste knitted cotton fabrics in the investigated stripping solution.(3)Oxidations on the ?-PbO2 electrode were mainly used for color stripping from dyed cotton fabrics when synthetic Reactive Black 5 wastewater was used as the stripping solution.Whilst on the Ti/TiO2-RuO2-IrO2 electrode simultaneously strip dye from dyed cotton fabrics and decolorize dye in stripping solution.The stripping percent of cotton fabrics after 15 min of stripping in 300 mg/L of Reactive Black 5,Reactive Red X-3B and Reactive Brilliant Blue KN-R solution were over 97.0%.Reactive Black 5 solution was reused for stripping of 9 pieces of dyed cotton fabrics dyed with Reactive Black 5.In the case of P-PbO2 electrode,the COD value of the stripping solution decreased with the increase of stripping times,whereas,in the case of Ti/TiO2-RuO2-IrO2 electrode,the COD value of the stripping solution firstly decreased and then slowly increased,showing the accumulation of dye molecules stripped from fabrics occurred.The FTIR analysis of the stripped cotton fabrics showed that the electrochemical stripping and the existence of Reactive dye in water had almost no effect on quality of stripped cotton fabrics.Electrochemical oxidation could also strip various dyes from waste cotton fabrics in the investigated stripping solutions.Therefore,electrochemical oxidation provides a cleaner and effective alternative for color stripping of dyed cotton fabrics and waste textiles.The stripping of dyes from the surface of dyed cotton fabrics and the electrochemical degradation of pollutants in water may occur simultaneouslym,which means that wastewater containing chloride ions could replace fresh water as stripping solution,which will reduce the consumption of fresh water and achieve the efficient treatment of wastewater.