Research On Salt Substitutes Of Reactive Dyeing And Recycling Of Dyeing Wastewater

Dye wastewater containes a large amount of inorganic salts (sodium chlorate orsodium sulfate) which are used as the accelerants in the dyeing process of reactive dyes.These salt agents are difficult to remove from wastewater and the treatment cost is high.Researchers have devoted themselves to solve this problem for direct discharge of thewastewater with high salinity will seriously pollute the ecological environment. Saltsubstitutes are new salt agents to replace inorganic salt in reactive dyeing process. Saltsubstitutes are easy to ecologically degrade and has low environmental pollution.There are a wide range of salt substitutes, and the present researches focus on sodiumcarboxylates. It is difficult to prepare and use salt substitute for the lack of systematicresearch. Therefore, accelerating mechanism of sodium carboxylate on reactive dyesand recycling of dyeing wastewater were studied in this thesis.Accelerating mechanism of sodium carboxylates were studied in the first part ofthis thesis. Firstly, cations and anions accelerating properity of different sodiumcarboxylate was studied, and compared with sodium sulfate and sodium chloride.Secondly, snynergistic effects of sodium sulfate and sodium chloride with differentsodium carboxylates were studied. Finally, accelerating mechanism ofanions werestudied. The results showed that cations play a major role in dyeing acceleration, andanions have some influences on the dyeing acceleration. For dyeing acceleration effect,formate ions are better than chlorine ions,and sulfate ions are better than oxalate ionswith same mol concentration. In the condition of the same mol concentration ofanions, the dyeing acceleration effect gets better as sodium ions increased. In thecondition of the same mass concentration, NaCl shows the best dyeing accelerationeffect. The above mentioned conclusions are proved to be correct by zeta potential testing of fiber surface. Inorganic salts can be reduced by compoundingwith organic salt, but dyeing acceleration effect was not obvious. Dyeing contrast testof carboxlate salts and binary carboxlate salts indicated that acceleration dyeing effectincreased with anionic molecular weight increasing in the condition of same sodiumion mol concentration. Taking dyeing effect and the amount of salt intoconsideration, sodium oxalate and sodium formate were suitable for replacing thetraditional inorganic salt.The application of sodium carboxylate (sodium oxalate and sodium formate)inreactive dyes dyeing was studied in the second part of this thesis.Firstly, the sodiumcarbonate effect in the dyeing process using sodium carboxylate and the influence ofdifferent electrolytes on the maximum absorption wavelength of the dye and non ionsurfactant cloud point were studied. The relationship between dyeing temperature andthe dosage of sodium oxalate in different dye concentration was studied by comparingdyeing exhaustion rate curves of different electrolyte. Secondly, the effect ofelectrolyte on the dyeing fabric fastness and color light. Finally, reactive red3BS oncotton fabric dyeing kinetics and thermodynamics using sodium formate were studied.The results showed that sodium oxalate had the same application as sodium sulfateduring reactive dyes dyeing, and sodium carbonate also should be used as fixing agent.Additionally, for dyeing fastness and color shade,sodium oxalate was same asinorganic salt. Sodium formate had no effect on the maximum absorption wavelengthof dye. Sodium formate had less effect on the Nonionic surfactant cloud point thansodium sulfate. Dye exhaustion rate of sodium formate was slightly lower than that ofsodium oxalate and sodium sulfate, and dye exhaustion rate of sodium oxalate wasslightly higher than that of sodium sulfate by comparing the dye exhaustion rate curve.Dyeing behavior of sodium oxalate and sodium formate were same as that of sodiumsulfate. Dyeing kenetics revealed dyeing acceleration effect of sodium formate wassimilar to that of sodium sulfate. Thermodynamics revealed adsorption of reactive dyeon cotton fiber using sodium formate and sodium sulfate all fitted the Freundlichadsorption isotherm.The adsorption enthalpy of sodium formate and sodium sulfatewere-20.50KJ.mol-1and-16.96KJ.mol-1respectively. Photocatalytic promoting effect of sodium carboxylate (sodium oxalate andsodium formate) was studied in the third part of this thesis. The study focused on thebest application condition of sodium oxalate and sodium formate in the photochemicalreaction using TiO2doped Ag as photocatalyst. Reactive red3BS photocatalyticdegradation kinetics of sodium sulfate system, sodium oxalate-sodium sulfate systemand sodium formate-sodium sulfate system in the best application condition werestudied. The result showed that the photocatalytic effect was best when theconcentration ratio of sodium sulfate and sodium carboxylate kept at2:1. And thelower the pH value, the higher the photocatalytic effect. When reactive red3BSphotocatalytic reaction condition was kept constant, the photocatalytic kinetics ofsodium sulfate system, sodium oxalate-sodium sulfate system and sodiumformate-sodium sulfate syetem were all fitted approximate negative first-order reactionkinetic relationship. The photocatalytic apparent rate constant of three system were0.004min-1,0.087min-1and0.479min-1. Sodium oxalate and sodium formate couldgreatly improve the photocatalytic decolorization rate.The reactive dyeing wastewater treatment was studied as follows: decolorizationâ†'purificationâ†'adjustment of pHâ†'determination of salinityâ†'reusing, which wasbased on the analysis of the reactive dyeing wastewater composition,in the fourth partof this thesis. The research focused on the screening of decolorizing agent and the lightrefractive index method for salt content testing. Finally, recycling method of reactivedyeing wastewater was explored. The results showed that decolorizing effect of stoveash was better than that of plant ash and briquette ash. Stove ash could also slightlyincrease the decolorizing effect of reactive dyes after alkali modification. Calciumhydroxide had wide adaptability in reactive dyes decolorization, high efficiency, shorttime. The treated wastewater didn’t substantially contain dye degradation products,which indicated that residual dye as a whole was removed. The method of lightrefractive index was suitable for salt content testing. There was a good linearrelationship between sanility and salt concentration in the solution of single salt, andthe salinity exhibited additivity in the solution of mixed salt. Dye concentration hadlittle effect on the determination of salinity. There was no obvious influence on dyeing effect when treated wastewater was recycled for dyeing three times under thisexperimental condition. Accelerating salt could be used repeatedly in this method. Itprovided reference for solving the inorganic salt pollution to the environment.