Manure treatment has become a focal issue in relation to current national policies on environmental and renewable energy matters. Heavy metals can be excreted with the animal manure, contributing to pollution of soil and water. Therefore, animal manure needs proper treatment before application to agricultural soils. Here, we review the species transformation of HMs and fate during incineration, pyrolysis, gasification and hydrothermal processing of animal manures. During thermal processes, 75%-90% of thermally stable HMs such as Cr, Ni, and Mn were concentrated in the solid-phase. HMs with less thermal stability such as Cd, As, Hg, and Pb are inclined to concentrate in the aqueous phase and gas phase, accounting for less than 5% of their total concentrations. In general, thermal processes transform HMs in the exchangeable fraction with high biotoxicity to oxidizable fraction or residual fraction with less bioavailability. In addition, the operating conditions and co-processing with other materials may influence the species transformation of HMs. Finally, recommendations for future research on the proper disposal and utilization of animal manure are proposed. More large-scale experiments are required to elucidate the precise mechanism behind the immobilization of HMs. The influence of additives (catalysts and HM stabilizers) and the influence of the type of solvent on HM transformation needs further study.

中文翻译：

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粪肥热处理过程中重金属的演变：重要评论和展望。

与当前有关环境和可再生能源问题的国家政策相比，粪便处理已成为焦点问题。重金属会随动物粪便排出体外，造成土壤和水的污染。因此，在施用于农业土壤之前，动物粪便需要进行适当的处​​理。在这里，我们回顾了动物粪便的焚烧，热解，气化和水热处理过程中的HMs和命运的物种转化。在热处理过程中，75％-90％的热稳定HM（例如Cr，Ni和Mn）集中在固相中。Cd，As，Hg和Pb等热稳定性较差的HMs倾向于集中在水相和气相中，占其总浓度的不到5％。一般来说，热过程将具有高生物毒性的可交换部分中的HMs转化为具有较低生物利用度的可氧化部分或残留部分。此外，操作条件和与其他材料的共处理可能会影响HM的物种转化。最后，提出了对动物粪便的合理处置和利用进行进一步研究的建议。需要更多的大规模实验来阐明固定HMs背后的确切机制。添加剂（催化剂和HM稳定剂）的影响以及溶剂类型对HM转化的影响需要进一步研究。提出了有关适当处理和利用动物粪便的未来研究的建议。需要更多的大规模实验来阐明固定HMs背后的确切机制。添加剂（催化剂和HM稳定剂）的影响以及溶剂类型对HM转化的影响需要进一步研究。提出了有关适当处理和利用动物粪便的未来研究的建议。需要更多的大规模实验来阐明固定HMs背后的确切机制。添加剂（催化剂和HM稳定剂）的影响以及溶剂类型对HM转化的影响还需要进一步研究。