The Study On The Speciation And Lability Of Cu/Zn In Poultry And Swine Manure-derived Biochar

Biochar is a kind of insoluble organic solid with strongly aromatic structure produced by thermal decomposition of biomass under limited or absence of oxygen supply at relatively low temperatures (<700C)。 Due to its widespread application, such as controlling greenhouse effect, using as soil amendment, adsorbing contaminants, etc, biochar has attracted global attention, especially the attention of western environmental scientists. The feedstocks of biochar are various. Animal manure as a kind of feedstocks generally contains high levels of Cu and Zn. But there are few studies about the mobility, bioavailability of heavy metals in biochar. In this study, the poultry and swine manure were pyrolysed in a temperature-controlled muffle furnace under limited or absence of oxygen supply at the temperature of200,300,400,500,700℃. Then the basic properties, speciation and lability of the heavy metals as affected by feedstock and pyrolysis temperature were studied, in order to provide technical supports for the utilization of animal manures, the application of biochar and the sustainable development of agriculture.The results showed that the yield of biochar decreased with the increase of pyrolysis temperature, and swine manure-derived biochar was with higher yield. The ash contents were41.2-70.6%for swine manure-derived biochar and20.3-48.1%for poultry manure-derived biochar. The FTIR indicated that the oxygen functional groups of biochar prepared at the lower temperatures (≤300) changed little compared with that of the feedstock, but decreased significantly above400℃. The mineral contents increased with the increase of pyrolysis temperature, despite the volatilization loss. The contents of Cu and Zn in swine manure-derived biochar were628-1033mg/kg and1121-1598mg/k, seperately. While the contents of Cu and Zn in poultry manure-derived biochar were184.04-398.17mg/kg and332-664mg/kg, separately. The contents of the heavy metals in biochars were closely related with its yields. The higher the yields, the smaller the enrichment factor of heavy metals would be. Different feedstocks had different yields and the heavy metals in poultry manure-derived biochar had bigger enrichment factor compared with that in swine manure-derived biochar.The results of sequential extraction showed that the predominant species of Cu in two kinds of biochar were the same, with the OM-Cu (bound to organic matter and sulfide) being the most important (73-92%) at the pyrolysis temperature of200-500℃, while the residue Cu was dominant (66-74%) at700℃. The speciation of Zn changed little among different ptrolysis temperatures.The predominant species of Zn was found in the Fe/Mn oxide fractions in both manures and biochars. But the contents of Zn bound to OM and sulfide increased at400,500℃; and the contents of residual Zn increased significantly at700℃. The XANES showed Cu K-edge energy (E0) was8990eV in the source material and8981eV in biochar. E0shift indicated that reduction of copper might involve in the pyrolysis process.The linear combinations of Cu K-edge XANES suggested that the majority of Cu were bound with organic groups(68-91%). But the resembling Cu-citrate species were clearly the major Cu species in the swine manure, while Cu-cysteine-like species increased in swine manure-derived biochar. Pyrolysis resulted in the appearance of CuO, and its percentage was as high as32.4%in the Z500. The Zn K-edge XANES spectra from the samples indicated that the valence state of Zn did not change during the pyrolysis process. The normalized k2-weighted EXAFS spectra for biochars were similar to the source materials, demonstrating that Zn molecular species did not greatly change in the low-temperature (300-500℃) pyrolysis process. However, ZnS increased by12-24%and ZnO increased by2.6-3.5%in biochar compared with source materials.Physiologically based extraction test (PBET), synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP) were performed on biochar. Results indicated that relative bioaccessibility of Cu and Zn in poultry manure-derived biochar decreased, but the relative bioaccessibility of Cu for swine manure-derived biochar prepared at300-700C increased.Both Cu and Zn leachability with SPLP decreased greatly with the increase of pyrolysis temperature. Concerning the speciation, the leachability and bioaccesibility of heavy metals, pyrolysis at500℃was appropriate for poultry and swine manures contained heavy metals.