Characterization of biochars from different sources and evaluation of release of nutrients and contaminants

Abstract

The biochar, product of pyrolysis of organic waste, has been used as a soil conditioner and alternative on
solid waste management. However, the raw material and pyrolysis temperature used influence the quantity and dynamics of
release of nutrients and contaminants from the biochar. The objective was to evaluate the use of waste sugarcane bagasse,
eucalyptus and sewage sludge for production of biochar and determine the chemical, physical, mineralogical properties and
acid extraction of these materials produced at 350 °C and 500 °C. Were evaluated the proportion of C, H, N, O; ashes; macro
and micronutrients, plus some contaminants; characterization of mineral phases by diffractometry of X- rays; functional
groups by infrared absorption spectroscopy (FTIR). Moreover, it was determined the release of nutrients and contaminants
for the extraction in increasing concentration of HNO3
(0,01 - 2,0 mol L-1). The O/C and H/C relations decreased with
increasing temperature of pyrolysis, which define a greater stability of the C of biochars. Sewage sludge biochar (BC-L) had
the highest nutrient release rates and contaminant metals (Cd, Cr, Ni and Pb). Acid extraction of other biochars was very low
(<20% of the total content). The results indicate that the carbon fraction of biochar contributes to the low rate of release of
the elements in acid place.