Journal
SCIENCE OF THE TOTAL ENVIRONMENT
Volume 658, Issue -, Pages 1306-1315Publisher
ELSEVIER
DOI: 10.1016/j.scitotenv.2018.12.269
Keywords
Biochar colloid; Aggregation; Water chemistry; Humic acid; XDLVO theory
Categories
Funding
- National Natural Science Foundation of China [41501232, 41771255]
- NIFA [1014527]
- National Key Research and Development Project [2017YFD0801503, 2016YFC0501902]
- Program of 1000-talents Plan for Young Researchers
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An understanding of biochar colloid aggregation and stability in aqueous environments is critical for assessing biochar fate and mobility in the soil. The aggregation kinetics of wheat straw-derived biochar colloids pyrolyzed at two temperatures 300 and 600 degrees C (WB300 and WB600 colloids, respectively) were investigated in monovalent and divalent electrolyte solutions in absence presence of humic acid (HA). Results show that the critical coagulation concentrations (CCCs) of WB300 colloids in NaCl and CaCl2 solutions were 274 and 61.4 mM, which were higher than those (183 mM for NaCl and 38.1 mM for CaCl2) of WB600 colloids. WB300 had more oxygen containing functional groups than WB600, which induced more negative surface charge on WB300. HA of 5 mg L-1 greatly increased the CCCs of WB300 and WB600 colloids to 1288 and 806 mM in NaCl solutions, but decreased the CCCs to 54.6 and 37.0 mM in CaCl2 solutions because of strong bridging between HA and Ca2+ In CaCl2 solutions with high salt concentrations (near to the CCCs), different HA concentrations caused distinct effects on the aggregation of biochar colloids. The aggregation of biochar colloids was accelerated by HA with the concentration higher than 5 mg L-1 through cation-bridging while the aggregation was inhibited in the presence of <2.5 mg L-1 HA. Our findings show that pyrolysis temperature used for biochar production had a large effect on the aggregation of biochar colloids in the aqueous environment and that cation type and dissolved natural organic matter are controlling variables. (C) 2018 Elsevier B.V. All rights reserved.
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