The treatment of waste water from cotton dyeing process and its preparation for re-use

[M. Šmelcerović]

XVI, 187 listova

Chemical technology of textile, Chemistry and chemical technology

The Ph.D. Thesis represents a complex study of several areas: the first is related to the optimization of dyeing cotton textiles with direct and reactive dyes, the second to the physical and chemical modification of natural waste materials (fly ash), the third to the possibility of applying modified natural adsorbent in the process of dye removal from the dyeing effluent, and finally, the fourth to the recirculation of discolored waste water back into the new textile dyeing process. Based on the results obtained, it can be concluded that the modified waste fly ash is an efficient adsorbent for the removal of reactive and direct dyes or combinations of two reactive or two direct dyes from aqueous solutions, with a reasonable tendency of the application under industrial conditions. Also, it is possible to reuse so discolored water, under industrial conditions, for the new textile dyeing. The study revealed the following results: 1) Optimization of cotton dyeing with Direct Blue 85 or Direct Red 79, showed savings of electrolytes, leveling agents, defoamers and temperature of dyeing; 2) Optimization of cotton dyeing with the mixture of Direct Blue 85 and Direct Red 79, had savings of electrolytes, leveling agents, defoamers and temperature of dyeing; 3) Optimization of cotton dyeing with Reactive Blue 222 or Reactive Red 194, demonstrated savings in the quantity of electrolyte, alkalis, defoamer, leveling agents, time and temperature of dyeing; 4) Optimization of cotton dyeing with the mixture of Reactive Blue 222 and Reactive Red 194, led to savings in electrolytes, defoamer, leveling agents and dyeing time; 5) Modification of the native fly ash was successfully applied in order to obtain the structure which is more effective to retain dye molecules by physical and chemical interactions; 6) X-ray powder diffraction showed that the dominant phase of the analyzed sample was calcium carbonate, followed by graphite, quartz and carbon; 7) Modified ash is relatively fine bulk material consisting of heterogeneous porous particles of diverse shapes and forms, generally below 10 microns in size; 8) The FTIR spectrum of the modified fly ash shows characteristic peaks, which correspond to the functional groups of the modified fly ash; 9) The higher differences in adsorption of dyes, as a function of solution pH, indicate that this parameter is of significant importance for the adsorption of applied dye; 10) The adsorption of dyes is faster at the beginning, and then becomes slower until the equilibrium concentration is reached after 60 min; during adsorption process, the dye concentration in the solution is reduced related to the weight of the modified fly ash, slightly more intense at higher initial dye concentrations; 11) The amount of adsorbed dye per unit mass of the modified fly ash increases with the duration of the adsorption process, the higher the temperatures give better results in all cases and, generally, the impact of temperature on adsorption is not significant; 12) Increasing the initial dye concentration decreases dye exhaustion in all cases, although the actual amount of dye adsorbed per unit mass of the modified ash increases with the initial concentration; the greater amount of adsorbent adsorbs more dye, while the temperature does not play a greater role; 13) The Langmuir adsorption model provides a very good description of the experimental data. The constants, the maximum amount of adsorbate that is able to be bound to the adsorbent, as well as the free energy of adsorption increase partly with the increase of temperature and of the amount of the modified fly ash; RL parameter confirms that the Langmuir isotherm is suitable for this specific case; 14) The Freundlich adsorption model can provide a sufficient description of the experimental data, but only slightly lower than the Langmuir model; the Freundlich constant KL indicates lower dye absorption and lower adsorption capacity of the adsorbent; the second Freundlich constant, n, shows that the dye is well adsorbed under all test conditions, and most preferably at higher amount of adsorbent; 15) The Jovanovic adsorption model delivers results with much lower functionality of variables, giving rise to the conclusion that there are lateral interactions in the monolayer that covers the adsorbent surface of the adsorbent, and that some chemical interactions exist in addition to the mechanical contact between adsorbed and desorbed molecules; "Trial-and-error" method of nonlinear regression applied to the Jovanovic model gave excellent results, i.e., nonlinear model follows experiment very well and properly describes the dye adsorption on modified fly ash; 16) The Halsey model provides relatively high functionality of variables, similar to previous models; the Halsey isothermal constant, KH (adsorption capacity) increases with increasing temperature and decreases with the amount of adsorbent, while empirical constants, nH (intensity of adsorption), confirms that the adsorption is mostly more intense at low temperatures as well as with larger amounts of the adsorbent; 17) The adsorption model of pseudofirst- order is not applicable for describing the sorption flow, because there is scattering around the ideal curve, while the nonlinear model of pseudo first order gave better results; 18) The dye adsorption on the adsorbent is sufficiently well described by the model of pseudo-second order; 19) The Model of intraparticle (interparticle) diffusion is partly involved in the process of adsorption although this model is not the only step that controls the adsorption but also diffusion through the pores and surface diffusion is dominating. 20) The Elovich model does not adequately describe experimental data compared to other models; 21) The positive values of the change in enthalpy (between 0.19 and 6.9 kJ / mol), indicate the endothermal nature of the adsorption interactions and stable energy process, numerical values have suggested that the adsorption could be mainly physical; 22) A positive value of entropy change indicates the increase of coincidences at solid - solution interface during the adsorption process and it increases with adsorbent amount and decreases with increasing adsorbate concentration and temperature; 23) The negative values of the free energy change confirm spontaneity of the process nature, i.e., indicate the favoring nature of the dye adsorption at 20, 40 and 600C, with a high potential; 24) The activation energy with values between 2.13 and 3.59 kJ/mol, assumes the fast reactions or that individual, structurally different parts of the adsorbent can take the role of a catalyst by lowering the activation energy of a chemical reaction; 25) The results showing the content of organic matter in water before and after discoloration, significantly lose their initial values related to colored wastewater, i.e., after adsorption process they are reduced 2.8 to 4.4 times; 26) The proposed models of waste water treatment I, II and III could be applied in practice, depending on the specific situation. The model I includes drainage, sedimentation, adsorption, filtration and neutralization with final aeration. The model II does not include precipitation and neutralization, but includes one more adsorption stage. Model III includes all procedures identical to the model II except mechanical mixing where 200 kHz ultrasound is used instead. 27) It is possible to reuse water purified according to the proposed models I - III, with an additional softening and possible correction of dyeing formulations for dyeing lighter shades; 28) The textile dyeing using treated water can give shades identical to the shades obtained by classical dyeing (in the presence of a new, fresh water).

otpadni pepeo, modifikacija, reaktivna boja, direktna boja, bojenje, adsorpcija, obezbojavanje, recirkulacija, jačina obojenja

waste fly ash, modification, reactive dye, direct dye, dyeing, adsorption, discoloring, recirculation, dyeing intensity

628.3 677.027

677.21:677.021.4]:628.3(043.3)

Elektronska teza