College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
J Environ Sci (China). 2019 Aug;82:192-202. doi: 10.1016/j.jes.2019.03.007. Epub 2019 Mar 20.
Hazardous waste dechlorination reduces the potential of creating dioxins during the incineration process. To investigate the salt effect on waste dechlorination, molten hydroxides with a low melting temperature were utilized for the pre-dechlorination and decomposition of chlorine-containing organic wastes (COWs) including trichlorobenzene (TCB), perchloroethylene, hexachlorobenzene and chlordane. The results showed that a eutectic mixture of caustic sodium and potassium hydroxides (41 wt.% NaOH and 59 wt.% KOH) led to a low melting point below 300°C and a relatively high chlorine retention efficiency (CRE) with TCB as a representative COWs. The amounts of hydroxides, reaction time, and temperature all had notable influence on CRE. When the mass ratio of hydroxides to TCB reached 30:1, approximately 98.1% of the TCB was destroyed within 2.5 hr at 300°C with CRE of 71.6%. According to the residue analysis, the shapes of reaction residues were irregular with particles becoming swollen and porous. The benzene ring and C-Cl bonds disappeared, while carboxyl groups formed in the residues. The stripped chlorine was retained and condensed to form chloride salts, and the relative abundance of the chloride ions associated with the mass of TCB in residues increased from 0 to 75.0% within the 2.5 hr reaction time. The observed concentration of dioxins in residues was 5.6 ngTEQ/kg. A reaction pathway and possible additional reactions that occur in this dechlorination system were proposed. Oxidizing agents may attack TCB and facilitate hydrogenation/dechlorination reactions, making this process a promising and environmentally friendly approach for chlorine-containing organic waste treatment.
危险废物脱氯可降低焚烧过程中二恶英生成的潜力。为了研究盐对废物脱氯的影响，利用低熔点熔融氢氧化物对包括三氯苯（TCB）、全氯乙烯、六氯苯和氯丹在内的含氯有机废物（COW）进行预脱氯和分解。结果表明，苛性钠和氢氧化钾的共晶混合物（41wt.% NaOH 和 59wt.% KOH）具有低于 300°C 的低熔点和相对较高的氯保留效率（CRE），以 TCB 作为代表性 COW。氢氧化物的用量、反应时间和温度对 CRE 都有显著影响。当氢氧化物与 TCB 的质量比达到 30:1 时，在 300°C 下，2.5 小时内约有 98.1%的 TCB 被破坏，CRE 为 71.6%。根据残留物分析，反应残留物的形状不规则，颗粒膨胀且多孔。苯环和 C-Cl 键消失，而残留物中形成了羧基。脱除的氯被保留并缩合形成氯化物盐，与 TCB 质量相关的氯离子的相对丰度在 2.5 小时的反应时间内从 0 增加到 75.0%。在残留物中观察到的二恶英浓度为 5.6ngTEQ/kg。提出了一种反应途径和可能在这个脱氯系统中发生的附加反应。氧化剂可能会攻击 TCB 并促进加氢/脱氯反应，使这个过程成为一种有前途的、环保的含氯有机废物处理方法。
