Abstract
Biochar (BC) is a carbon-rich product obtained when biomass is thermally decomposed at relatively low temperatures (under 700ºC) and limited supply of oxygen in a process called pyrolysis. Because of its porous structure, charged surface and surface functional groups, BC exhibits a great potential as an adsorbent. Its characteristics strongly depend on the feedstock and the pyrolysis conditions, in which the temperature is the key parameter. The aim of this study was to evaluate the adsorption potential for the removal of uranium, U(VI), from aqueous solutions using BC obtained through the pyrolysis of the macauba coconut endocarp as a function of the final pyrolytic temperature. The influence of parameters such as pH, sorbent dose and initial concentration on the adsorption of U(VI) was investigated. The maximum adsorption capacity (q) was achieved for the BC obtained at 250°C (BC250), which presented a removal percentage of approx. 86%, demonstrating the potential of the BC from macauba endocarp for treatment of wastewaters.
Highlights
Radioactive uranium aqueous wastes emerge as a result of many distinct nuclear activities such as mining, research, fuel cycle and nuclear medicine
The influence of parameters such as pH, adsorbent dose and initial concentration on the adsorption of U(VI) was investigated for the macauba biochar obtained at 350 °C (BC350) in order to optimize the adsorption conditions for the removal of U (VI) from aqueous solutions
The gravimetric yield obtained for BC350 was of 46.09 % and the fixed carbon content was of 60.22 %, rendering a gravimetric yield factor of 0.28 %, which, by comparison, qualified 350 °C as the operational highest treatment temperature (HTT)
Summary
Radioactive uranium aqueous wastes emerge as a result of many distinct nuclear activities such as mining, research, fuel cycle and nuclear medicine. Combined techniques and operations such as chemical precipitation, reverse osmosis, solvent extraction, micellar ultrafiltration and adsorption are normally required for the treatment of uranium contaminated wastewaters and liquid radioactive wastes [2, 3]. Several studies have demonstrated that biochar can be applied for wastewater treatment because it effectively removes heavy metals from aqueous solutions [13, 14]. Residence time and temperature have a direct impact in the distribution and yield of each of the biochar [20, 21] Of these parameters, the maximum temperature to which the biomass is subjected in the pyrolysis reactor, called highest treatment temperature (HTT) has the greatest overall influence on the biochar properties [22, 23, 24]. The selection of the optimal parameters is part of the preliminary studies which allow to maximize the BC’s performance, being very important, for the application itself, but for the realization of further experiments and characterizations
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