Abstract:

The rapid growth of municipal solid waste incineration in China has led to a sharp increase in the production of air pollution control (APC) residues. Potential environmental risks such as heavy metal leaching and dioxin release restrict the resource utilization of fly ash. This paper investigates the impact of adding NaH₂PO₄ during the water washing process on the pollution characteristics of the products from washing and thermal treatment (600℃ and 700℃) of APC residues. The results show that the addition of sodium dihydrogen phosphate reduces the leaching of Cl, Pb, Ba, and Se, but promotes the leaching of As and Cr during the APC residues washing process. When the addition of NaH₂PO₄ is no less than 5.0%, the leaching concentration of Pb in washed fly ash meets the limit values listed in Technical Specification for Pollution Control of Fly-ash from Municipal Solid Waste Incineration (HJ 1134—2020). Pb is the most abundant heavy metal in the wash liquor. Adding 5.0% sodium dihydrogen phosphate can reduce the Pb concentration in the wash liquor to below 10 mg/L. The washing-thermal treatment process promotes the volatilization of elements such as Pb, Cu, and Cd in APC residues, but the heavy metal leaching concentration of thermal-treated washed APC residues is low, meeting the corresponding standard limits. The temperature is identified as an important factor affecting the volatilization of heavy metals in washed APC residues, and less volatilization was observed under 600℃. After thermal treatment under 700℃, the content of Pb in washed fly ash is reduced from (1700±100) mg/kg to (320±80) mg/kg. The addition of NaH₂PO₄ inhibits the volatilization of chlorides and sulfates, but has no significant effect on the change of leaching characteristics of washed APC residues during thermal treatment. The research results provide scientific basis for the in-situ treatment of washed APC residues in the incinerator, which is beneficial for the source reduction, harmlessness, and utilization of APC residues.

Key words: leaching toxicity, thermal treatment, leaching, desalination, air pollution control residues, municipal solid waste incineration, environment

摘要：

我国生活垃圾焚烧处置的快速增长使得飞灰产生量急剧增加。潜在的重金属溶出、二英等环境风险制约着飞灰的资源化利用。通过在水洗过程添加磷酸二氢钠，探究了磷酸二氢钠对飞灰水洗和热处理（600℃和700℃）产物污染特性的影响。结果表明，添加磷酸二氢钠可抑制飞灰水洗过程中Cl、Pb、Ba和Se的溶出，但对As和Cr的溶出存在促进作用。当药剂添加量不少于飞灰的5.0%时，加药水洗飞灰的Pb浸出浓度能够满足《生活垃圾焚烧飞灰污染控制技术规范（试行）》（HJ 1134—2020）标准限值的要求。水洗液中含量最多的重金属是Pb，添加5.0%磷酸二氢钠可使水洗液的Pb浓度降低至10 mg/L以下。水洗-热处理过程促进了飞灰中Pb、Cu、Cd等元素的挥发，但水洗-热处理飞灰的重金属浸出浓度较低，满足相应的标准限值要求。热处理温度是影响水洗飞灰中重金属挥发的重要因素，600℃热处理有利于控制重金属挥发。700℃处理后，水洗飞灰的Pb从（1700±100）mg/kg降低至（320±80） mg/kg。磷酸二氢钠的添加有利于减少热处理过程中氯盐和硫酸盐的挥发，而对水洗飞灰热处理前后的重金属浸出特性没有显著影响。研究结果为水洗飞灰在焚烧炉内原位处理提供了科学依据，有利于飞灰的源头减量、无害化和资源化。

关键词: 浸出毒性, 热处理, 浸出, 脱盐, 飞灰, 生活垃圾焚烧, 环境