Copper Speciation Evolution in Swine Manure Induced by Pyrolysis Yuan Cheng, Lei Luo,* Jitao Lv, Gang Li, Bei Wen, Yibing Ma, and Rixiang Huang Cite This: Environ. Sci. Technol. 2020, 54, 9008-9014 Read Online ACCESS Metrics & More Article Recommendations *sı Supporting Information ABSTRACT: Swine manures generally contain high levels of copper (Cu) resulting from its use as a growth promoter in feedstuff. Pyrolysis can further concentrate Cu whereas decrease its available fraction in swine manures. Here we investigated the speciation transformation of Cu and associated elements in swine manures induced by pyrolysis using multiple X-ray absorption spectroscopies. Results showed that over 82% of Cu existed as Cu(I)-S and Cu(I)-thiolate complexes in swine manures, which were transformed into stable Cu(I) 2 S during pyrolysis at a low temperature of 300 °C and partially oxidized and desulfurized into Cu(II) compounds at a high temperature of 500 °C. The speciation evolution of Cu in swine manures was consistent with the speciation distribution of sulfur in feedstuff and its following changes in swine manures during pyrolysis. About 58% of phosphorus existed as CaHPO 4 and struvite in swine manures, which were gradually transformed into stable Ca-bound species such as hydroxyapatite during pyrolysis. The formation of stable phosphate, together with concentrated carbonates, significantly decreased the available Cu in pyrolyzed manures. These findings suggested that the high levels of S and P in feedstuff profoundly affected the speciation of Cu in the swine manures and derived biochars. This study has important implications to our understanding of the behaviors of heavy metals in manure-derived biochars once entering soil environments. ■ INTRODUCTION Application of livestock manures to agricultural soils can pose risks to human and ecosystem health because of a vast variety of hazardous materials commonly present in the manures. 1-5 Particularly, the abuse of copper (Cu) as a feedstuff additive has caused over 61% swine manure samples exceeding the threshold value for Cu (85 mg/kg) in China, in reference to the current limits of manure compost, 6 based on our investigation. 3 Conversion of livestock manures into biochar via pyrolysis is proposed as a promising biowaste treatment alternative because of multiple benefits such as pathogen and organic contaminant decomposition, waste volume reduction, carbon sequestration, and heavy metal immobilization. 7-11 However, heavy metals in livestock manures are generally enriched after pyrolysis, 1,2,12 which may exacerbate potential health and environmental risks following land application of the treated products. With rapid growth in livestock production and global interests in the application of biochars in soil environments, understanding the behaviors of heavy metals in swine manures induced by pyrolysis is necessary for guiding proper manure treatments and applications. Toxicity of heavy metals largely depends on their chemical nature rather than their concentration. 6 Therefore, speciation of heavy metals in swine manures, i.e., their oxidation state, mineralogy, complexation environment, and chemical extract- ability, is useful for predicting their mobility, bioavailability, and fate in the environment. 4,13 Multiple species of Cu with different valence states may exist, such as in forms of sulfur- and/or organic carbon-complexed compounds, in swine manures and derived biochars. 4,13 For instance, Cu mainly exists in the form of sulfide compounds (Cu 2 S) with a Cu(I) oxidation state in fresh swine manures, which can facilitate the accumulation of Cu in soil when applied to soil environments since sulfide compounds of Cu are very insoluble. 14 Cu can also exist as organic carbon-bound complexes in swine manures which are more bioavailable compared to sulfide compounds. 14-16 Many studies 1,2,8,12 have demonstrated that pyrolysis can decrease the environmental risks of Cu by significantly decreasing available Cu content in swine manures based on chemical extraction methods. A few studies have indicated that Cu(II) in swine manures can be reduced into Cu(I) and form Cu(I)-S complexes during pyrolysis. 4,17 However, chemical extraction cannot reflect the speciation distribution of Cu in the pyrolyzed manures at molecular Received: December 3, 2019 Revised: April 6, 2020 Accepted: June 15, 2020 Published: June 15, 2020 Article pubs.acs.org/est © 2020 American Chemical Society 9008 https://dx.doi.org/10.1021/acs.est.9b07332 Environ. Sci. Technol. 2020, 54, 9008-9014 Downloaded via RESEARCH CTR ECO-ENVIRONMENTAL SCI on July 24, 2020 at 05:09:32 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.