- Title
- Pyrogenic carbon and its interaction with heavy metals
- Creator
- Qi, Fangjie
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2017
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Pyrogenic carbon (PyC), the residue from incomplete combustion of fossil fuel and biomass, has been recognized as a strong geosorbent for soil contaminants. This research was designed to investigate the interaction of both soil native PyC and synthetic PyC (biochars) with heavy metals, particularly, cadmium (Cd). Soil native PyC are solid residues of heat-transformed organic matter (fossil fuel or biomass) that already exist in the natural environment while biochars are purposely manufactured carbon-rich products from thermochemical processing of biomass. The work includes quantification of soil native PyC and assessing its effect on the mobility of Cd in soils as well as examination of effects of biochars on sorption, mobility, pore water chemistry and bioavailability of Cd in soils with varying types. Based on a chemo-thermal oxidation method, we found PyC in Australian soils ranged from 0.27-5.62 mg/g (N=27), with it ranging from 2.58-5.62 mg/g in three Dermosol soils. Contribution of PyC to the total organic carbon (TOC) in the 30 soils was generally 2.0-11% (N=29), but in one Ferrosol soil reached as high as 26%. PyC was concentrated either in the top (0-10 cm) or bottom (30-50 cm) soil layers, with the highest PyC : TOC ratio in the bottom (30-50 cm) soil horizon in all soils. Based on the PyC and TOC quantified, we found soil native PyC and TOC did not exhibit significant correlation (N=18) with soil pore water Cd level but soil pH and CEC showed significant (p<0.05) negative correlation (N=18) with that. This suggests that soil inherent PyC and TOC were not the controlling factors for Cd solubility in soils but pH and CEC played the dominating role in governing Cd solubility (N=18). Hence, the following chapters (chapter 4, 5, 6) focused on soil external PyC, biochars, only. Biochars, like the studied wood shaving (WS, 650 °C) biochar and chicken litter (CL, 550 °C) biochar, are mostly likely to lose almost all of the organic C phases during natural fire combustion (200-500 °C), indicating low thermal stablity. However, the combusted WS and CL biochars retained considerable amounts of negative charge and displayed higher sorption for Cd (from 5.46 to 68.9 mg/g for WS and from 48.5 to 60.9 mg/g for CL). The increased sorption capacity of acidic WS biochar was due to increased pH (from acidic to alkaline) and the high sorption capacity of the remaining mineral components while that of CL biochar was because of the sorption from remaining mineral residues. The combusted biochars displayed stronger chemisorption (surface complexation and precipitation) for Cd compared to the weaker physiosorption (electrostatic reaction) from WS biochar and surface complexation and cation exchange from CL biochar. Hence, our study indicates that though not thermally stable, once subjected to potential natural wildfires, biochars can still have a high sorption capacity for Cd that may afford long-lasting retention due to the remaining mineral phase. This research also comprehensively examined functions of acidic and neutral biochars for their benefits as a soil amendment for the first time. We found that the studied acidic C rich WS biochar hold little agricultural or remedial values but was favourable for biochar-C sequestration into soils. The mineral rich neutral CL biochar may provide short-term agricultural benefit and certain sorption capacities of lower sorption capacity soils, but may be unlikely to result in heightened C sequestration in soils. The investigation of the acidic and neutral biochars on Cd solubility and bioavailability indicates acidic biochars may play its value in reducing Cd solubility under acidic conditions and neutral CL biochar can be effective in reducing Cd solubility and bioavailability in both neutral and acidic conditions. Neutral CL biochar was superior to acidic WS biochar in terms of reducing soluble (pore water), bioavailable (CaCl2 extractable) and bioaccessible (PBET extractable) Cd while WS biochar could outperform CL biochar in reducing mobility of Cd under acidic conditions (TCLP) in some soils while interior to CL biochar in other soils. During all of the soil factors, pH was found to control pore water Cd concentration. However, biochar did not reduce Cd solubility and bioavailability in lower sorption capacity soils through increasing pH or TOC. Benefits can be obtained from a certain period of ageing of biochar-amended soils to allow for both soils and biochars to fully play the immobilizing roles. This research suggests that more work needs to be done in the future regarding soil native PyC quantification and its interaction with heavy metals. Regarding biochars for heavy metal management, a systematic understanding about the reaction mechanisms and influencing factors is essential to select proper biochars for different contaminated cases. This research strongly encourages the pre-tests of biochars for the targeting use before large-scale production.
- Subject
- pyrogenic carbon; biochar; black carbon; heavy metal; soil
- Identifier
- http://hdl.handle.net/1959.13/1349807
- Identifier
- uon:30445
- Rights
- Copyright 2017 Fangjie Qi
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT01 | Thesis | 2 MB | Adobe Acrobat PDF | View Details Download | ||
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