Physicochemical study of dye removal using electro-coagulation-flotation process

The performance of electro-flotation with aluminum electrodes for the removal of different dyes from synthetic aqueous solutions and real wastewater was studied. Parameters affecting the electro-coagulation-flotation process, such as pH, initial dye concentration, treatment time and temperature were investigated. The maximum dye removal from synthetic solutions was achieved at pH 7. The order of the dye removals is nonionic>cationic>anionic. The removal process follows pseudo first-order kinetics and the adsorption follows both physical and chemical adsorptions which is exothermic. Negative values of entropy change, ΔS°, and Gibbs free energy change, ΔG°, indicate that this adsorption process is spontaneous and less favorable at high temperatures. Treatment of a real wastewater from textile dyeing factory showed that the removal efficiency was ranging between 92-99% for all constituents. The energy consumption is 0.0167 kWh/dm3

Influence of the structural modification of polycarboxylate copolymer with a low dispersing ability on the set-retarding of Portland cement

Two structurally modified polycarboxylate (PC) copolymers were synthesized to explore the influence of structural modification with these polymers on the set-retarding of Portland cement. The dispersion ability of these polymers was eliminated by introducing very short graft side chains. The synthesized copolymer structures were verified by FTIR, GPC and 1H NMR analyses. The initial and final setting times, polymer adsorption capability, strength development, paste fluidity, and XRD of hardened pastes were tested. The test results indicate that the PC copolymers do not increase the cement paste fluidity due to their short graft side chain length, while a significant set-retarding effect is observed when the polymer structure is highly anionic, with the set-retarding effect increasing linearly with polymer dosage up to 1%. The adsorption of copolymer on cement grains rapidly reaches saturation within 5 minutes after mixing for both polymers. Adding these PC copolymers does not noticeably change the early strength development, although the polymers selectively affect the hydration behavior of C3S and C2S at very early ages. Early hydration of groups, such as C3S, C2S, C3A and C4AF, is not likely to be significantly involved in the mechanism by which carboxylate copolymers with very short graft chains delay cement setting.close0