Simulated geochemical weathering of a mineral ash-rich biochar in a modified Soxhlet reactor.
Although there are many studies on the characterization of C in biochar and its C sequestration potential, there is little knowledge on the mineral fraction in biochar and its weathering. The latter, however, can have powerful implications on nutrient availability. In the present study, a modified Soxhlet reactor was used to simulate the long-term geochemical weathering of an ash-rich biochar produced from sewage sludge of a non-industrial area in New Zealand. The weathering process took place during a period of 300 h, with and without the addition of humic acid (1.00 g added to 20.00 g of biochar), and the treatments were referred to as treatment BC-HA and BC-B, respectively. Both the leaching kinetics and the transformations within the solid phase were studied. The results revealed that substantial amounts of K (8.5-10.2%) and S (20.2-28.3%) were recovered in the weathering solutions. Noticeable Ca (17.9-20.7%) and P (15.4%) in the solid were released but only a few were recovered in the weathering solutions because of the precipitation. The presence of humic acids increased this dissolution and thus the availability of K, S, Ca, Mg and P, but induced N immobilization. Nitrogen availability was already very low (<1.0% of the total N) due to the probable recalcitrant heterocyclic N structure. The pH of the biochar samples dropped from 8.4 to 7.5; this was mainly attributed to loss of base cations through leaching and probable carbonation of the system. The XPS spectra evidenced the oxidation of C in biochar during the weathering process with the formation of carbonyl and carboxylic functional groups. The results obtained in this study showed some promise for the positive use of modified Soxhlet extractor in simulating the geochemical weathering in ash-rich biochars and providing a better understanding on the kinetics of nutrient release. This will be key information in assessing the added value of biochars as soil amendments.
Yao
F X
FX
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, PR China. fyao@neiker.net
Arbestain
M Camps
MC
Virgel
S
S
Blanco
F
F
Arostegui
J
J
Maciá-Agulló
J A
JA
Macías
F
F
D001639:Bicarbonates / Q000032:analysis / Q000737:chemistry; D002118:Calcium / Q000032:analysis / Q000737:chemistry; D002254:Carbonates / Q000032:analysis / Q000737:chemistry; D002606:Charcoal / Q000737:chemistry*; D005591:Chemical Fractionation; D004864:Equipment and Supplies; D006812:Humic Substances / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000032:analysis / Q000737:chemistry; D008903:Minerals / Q000032:analysis* / Q000737:chemistry; D008956:Models, Chemical; D010710:Phosphates / Q000032:analysis / Q000737:chemistry; D011188:Potassium / Q000032:analysis / Q000737:chemistry; D012722:Sewage / Q000737:chemistry; D013455:Sulfur / Q000032:analysis / Q000737:chemistry; D014887:Weather
D001639:Bicarbonates; D002254:Carbonates; D006812:Humic Substances; D008903:Minerals; D010710:Phosphates; D012722:Sewage; C540010:biochar; D002606:Charcoal; D013455:Sulfur; D008274:Magnesium; D011188:Potassium; D002118:Calcium