Comparative Effect of Acid Treatment and DTPA Chelating Agent on Optical Properties of Chemi-Mechanical Pulp Bleached by Hydrogen Peroxide-Magnesium Hydroxide

Appropriate composition of chemicals and optimizing of bleaching stages have important effect on bleached pulp quality. Transition metals have the greatest destructive effects on peroxide bleaching. One of the most effective of treatments for removing these metals is using of chelating agents. Since in some countries, the chelating material is classified as toxic substances. This research was done for evaluating effectiveness and the possibility of using acidic pre-treatment as an alternative for chelating materials in hydrogen peroxide bleaching of CMP based on Mg(OH)2. Evaluation of optical properties of the hand sheet papers for pretreatment by DTPA and acid washing showed that the DTPA pre-treated samples had the highest brightness and the lowest yellowness index and opacity. Also, transition metals measurements showed that the acid pre-treatment removed more magnesium ion and less Mn and Fe ions compared to DTPA. According to the research results, acid pre-treatment have less efficiency in metal elimination than DTPA.