Efeito da adição de biocarvão de dejeto de suíno a um Neossolo Quartzarênico na sorção de zinco e cádmio

Abstract

Agroindustries generate organic waste that can have serious environmental impacts because the residues are usually disposed of in soils, causing accumulation of heavy metals, like cadmium and zinc, among other problems. This problem aggravates when residues are left in sandy soils which are very susceptible to erosion and have a low sorption capacity. Therefore, pollutants are transported vertically, into the soil profile, but also laterally, where they can contaminate adjacent sites and receiving waterways. The conversion of organic waste, such as swine manure, into biochar is a good alternative to reduce the risk of site contamination and to mitigate the environmental impacts agriculture. For that reason, this work aimed to evaluate the capacity of a sandy soil, that was treated with different doses of swine manure biochar (BDS), in zinc and cadmium sorption. Soil samples from the top soil layer (0-20cm) were collected from a commercial agricultural area located in Campo Verde, Mato Grosso. Doses of 0, 0.25, 0.75, 1.5 and 3% (w/w) swine manure biochar, obtained at 400ºC, were applied to the soil and incubated for 30 days at 60% field capacity. After this period, soil chemical and physical properties were analyzed, and two batch sorption assays were carried out, which consisted in adding to the soil, aqueous solutions of zinc (ZnCl2) and cadmium (CdCl2) at concentrations of 0, 2.5, 5, 10, 50 and 100 mg L-1 . Results showed that biochar additions increased the amount of macro and micronutrients, pH and soil organic carbon (labile and non-labile). Additionally, the soil had a large adsorptive capacity for Zn, but only moderate for Cd, and this capacity increased with the BDS doses. Zn and Cd sorption followed the Freundlich isotherm model. For both metals, and when biochar was applied, the sorption mechanism was a chemisorption. However, when biochar was not applied to the soil, the sorption mechanism for Cd was a physisorption.