Color removal from dye-containing wastewater by magnesium chloride

Color removal by MgCl2 when treating synthetic waste containing pure dyes was studied. The color removal efficiency of MgCl2/Ca(OH)2 was compared with that of Al2(SO4)3, polyaluminum chloride (PAC) and FeSO4/Ca(OH)2. The mechanism of color removal by MgCl2 was also investigated. The experimental results show that the color removal efficiency of MgCl2 is related to the type of dye and depends on the pH of the waste and the dosage of the coagulants used. Treatment of waste containing reactive dye or dispersed dye with MgCl2 yielded an optimum color removal ratio when the pH of the solution was equal to or above 12.0. For both the reactive and dispersed dye waste, MgCl2/Ca(OH)2 was shown to be superior to MgCl2/NaOH, Al2(SO4)3, PAC and FeSO4/Ca(OH)2 for color removal. A magnesium hydroxide precipitate formed at pH values greater than 12.0, which provided a large adsorptive surface area and a positive electrostatic surface charge, enabling it to remove the dyes through charge neutralization and an adsorptive coagulating mechanism. So, the MgCl2/Ca(OH)2 system is a viable alternative to some of the more conventional forms of chemical treatment, especially for treating actual textile waste with high natural pH.