Use of agricultural and agroindustrial residues as alternative adsorbents of manganese and iron in aqueous solution

Abstract The increase in the volume of agricultural and agroindustrial waste, associated with improper disposal, is a growing worldwide problem. The recovery of those residues is of crucial importance, since it reduces environmental impacts, protects public health, and allows the addition of value to the materials. One of the ways of exploiting adsorbents is related to the capacity of some wastes to be used as alternative adsorbents in the efficient removal of microcontaminants in aqueous systems. This work assessed the use of agricultural and agroindustrial residues: maize straw, wheat straw, soybean straw and soybean hulls for the production of alternative adsorbents to remove iron (Fe) and manganese (Mn) in water. For each residue investigated, two different polymers were obtained for use as adsorbents, a natural polymer (cellulose/lignin) and an EDTA-modified polymer (ethylenediaminetetraacetic acid). The adsorbents were characterized through FTIR (Fourier transform infrared spectroscopy) and nitrogen content. To evaluate the efficiency of the adsorbents, kinetic tests in batch mode and determination of Lagergren pseudo-first and pseudo-second order kinetic constants were performed. The results found that the modified polymer obtained from soybean hulls (SHE) showed increased Fe (96%) and Mn (88%) removal rate, in which the pseudo-second order kinetic model presented closer results between the experimental adsorption rates and the calculated ones for the two microcontaminants under study. In general, the modified soybean hulls proved to be a promising alternative adsorbent for the removal of iron and manganese in water treatment.

摘要 农业与农用工业废弃物产量持续攀升，加之处置失当，已成为日益严峻的全球性难题。回收利用此类废弃物至关重要，既可降低环境影响、保障公众健康，还能为相关材料提升附加值。其中一类资源化利用路径为利用部分废弃物作为替代吸附剂，实现水相体系中微污染物的高效去除。本研究针对玉米秸秆、小麦秸秆、大豆秸秆与大豆皮四种农业及农用工业废弃物，评估其用于制备替代吸附剂以去除水中铁（Fe）与锰（Mn）的可行性。针对每种受试废弃物，分别制备了两类聚合物吸附剂：天然聚合物（纤维素/木质素）与乙二胺四乙酸（ethylenediaminetetraacetic acid, EDTA）改性聚合物。通过傅里叶变换红外光谱（Fourier transform infrared spectroscopy, FTIR）和氮含量测定对吸附剂进行了表征。为评价吸附剂的吸附性能，开展了批次动力学实验，并测定了Lagergren准一级与准二级动力学常数。结果显示，由大豆皮制备的EDTA改性聚合物（SHE）对铁（96%）和锰（88%）的去除率均有所提升，且准二级动力学模型与两种目标微污染物的实验吸附速率和计算拟合结果更为吻合。总体而言，改性大豆皮是一种极具应用前景的替代吸附剂，可用于水处理过程中铁与锰的去除。