Influence of nickel during the thermal degradation of pine cone shell. Study of the environmental implications

Abstract Thermal valorization of heavy metal impregnated biomass has grown up as a researching field during the last few years; however the use of these contaminated wastes as fuel still presents several economic and technical drawbacks. Specially, insertion of nickel metal into the biomass during an impregnation stage with aqueous solutions of nickel salts, promotes wide dispersion of the precursor inside the lignocellulosic matrix and impacts on good results with respect to the reduction of tars. Therefore, the catalytic effect of the nickel during the thermal decomposition of an impregnated pine cone shell is investigated in this work. The effects of the heating rate and the atmosphere on the thermal decomposition of the natural solid show that an increase in heating rate produces a shifting of the curves at higher temperatures without significant change of its shape. Three distinct stages of mass loss are presented during degradation process for the different reaction atmospheres; however, the temperature ranges in which the stages are performed are different. Moreover, an increase in the thermal stability of nickel-loaded pine cone shell in the early stages is observed. The results obtained by mean method of Coasts-Redfern show that the function that could represent the thermal degradation mechanism associated with the major step of degradation of the pine cone shell is the reaction of nth order, being the third, fourth or fifth order the most regular order. About the environmental implications, the residual waste is lower for nickel-loaded biomass. Moreover, the nickel remains mainly in the ashes, therefore, the nickel content in these ashes may be recovered, or ashes distribute to any subsequent application.