Abstract Recently, a new type of bleaching sequence, Elemental Chlorine Free (ECF) light with one D stage, has been developed. It combines the efficiency and high selectivity of chlorine dioxide (ClO2) bleaching with more environmental friendly oxygen based bleaching chemicals. This work examines the effect of pH on the formation of adsorbable organically bound halogens (AOX) in an intermediate D stage – a single ClO2 stage at the middle of an ECF light bleaching sequence. Carbon dioxide (CO2) is used to generate a bicarbonate buffer in situ, stabilizing the pH during the bleaching. Near-neutral pH is hypothesized to decrease the formation of strongly chlorinating species, so that the AOX formation is reduced. The results indicate that a near-neutral pH D stage can reduce the AOX content in the effluents with up to 30%. The ISO brightness was unchanged to a lower ClO2 consumption. The pulp viscosity was slightly higher after near-neutral pH D stage, but to its disadvantage a lesser delignification and removal of HexA was obtained. The degradation of HexA correlated well with the AOX, affirming earlier theories that HexA has a major impact on the AOX formation. The higher amounts of residual HexA and lignin resulted in more thermal yellowing of the pulps bleached with a near-neutral pH D stage.

中文翻译：

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在接近中性 pH 值的二氧化氯漂白针叶木牛皮纸浆时减少可吸附有机结合卤素 (AOX) 的形成

摘要 最近，开发了一种新型的漂白程序，即具有一个 D 阶段的无元素氯 (ECF) 光。它将二氧化氯 (ClO2) 漂白的效率和高选择性与更环保的氧漂白化学品相结合。这项工作检查了 pH 值对中间 D 阶段（ECF 光漂白序列中间的单个 ClO2 阶段）中可吸附有机结合卤素 (AOX) 形成的影响。二氧化碳 (CO2) 用于原位生成碳酸氢盐缓冲液，在漂白过程中稳定 pH 值。假设接近中性的 pH 值会减少强氯化物质的形成，从而减少 AOX 的形成。结果表明，接近中性的 pH D 阶段可以将流出物中的 AOX 含量降低多达 30%。ISO 亮度保持不变，ClO2 消耗量较低。在接近中性的 pH D 阶段后，纸浆粘度略高，但不利的是，脱木素和 HexA 的去除较少。HexA 的降解与 AOX 密切相关，证实了早期关于 HexA 对 AOX 形成有重大影响的理论。较高量的残留 HexA 和木质素导致在近中性 pH D 阶段漂白的纸浆发生更多的热变黄。