Yield loss during bleaching of pulp of Pinus radiata previously delignified with oxygen

The pulp bleaching process removes or transforms the chromophore groups in the pulp, so that the final product reaches a desired brightness. However, this chemical treatment inevitably results in yield loss. Therefore, the objective of this work was to quantify the yield loss caused during the bleaching of kraft pulp of Pinus radiata delignified with oxygen. The material was submitted to three distinct ECF sequences (D₀(EPO)D₁D₂, D₀(EPO)D₁P, and Z/EDP). At the end of each bleaching stage, the pulp brightness and the loss of gravimetric yield of the process were determined, and the generated filtrates were collected. From these filtrates, the pollutant load of the effluent was determined by measuring the content of total dissolved solids, the chemical oxygen demand, the concentration of total organic carbon carbon, and the adsorbable organic halogens. Among the whole sequences, the Z/EDP sequence had the lowest gravimetric yield, the highest pollutant load in the collected filtrate, and lowest potential for adsorbable organic halogens generation. There was good correlation between the loss of yield from the bleaching process and the organic load of the generated effluent; and among the techniques studied, the quantification of total organic carbon was the most appropriate method for the indirect quantification of the yield loss during the bleaching process of the studied material.