Study of physico-chemical properties in the evaluation of adsorption in biochar produced from leaves of amendoeira-da-praia

ABSTRACT This study evaluated the physical-chemical properties of the adsorption process in biochar produced from dry leaves of beach-almond, Terminalia catappa, as a useful tool for remediation purposes in water contaminated with metals. The biochar was characterized by having: bands of O-H, CH2, C-O, and C-O-C; contents of 48.8% carbon, 46.6% oxygen, 3.3% hydrogen and the others between sulfur and nitrogen; the presence of macropores; and being sieved (100 mesh). Parameters such as pH, equilibrium time and adsorption capacity by the Langmuir and Freundlich isotherms were determined from experiments using a radiotracer cocktail (Co-57, Mn-54 and Zn-65) which was added to deionized water and a constants mass of biochar. The high-purity germanium detector (HPGe) was used to quantify the radiotracer activity by gamma spectroscopy. The results showed better adsorption from pH 3.8 and 30 minutes equilibrium time. The Langmuir and Freundlich isotherms had a good model fit, with n values higher than 1, and showed affinity between the metals and the biochar. The adsorption capacities of Zn-65, Co-57 and Mn-54 were 1.273 ng.g−1, 3.271 ng.g−1 and 9.026 ng.g−1, respectively.摘要 本研究针对以榄仁树（Terminalia catappa，俗称海滨杏仁）干燥叶片制备的生物炭（biochar）的吸附过程理化特性展开评估，将其作为修复重金属污染水体的实用手段。该生物炭的表征结果显示：其表面存在O-H、CH₂、C-O及C-O-C特征官能团吸收带；元素组成为碳48.8%、氧46.6%、氢3.3%，其余为硫与氮元素；具备大孔结构；且经100目筛分处理。通过向去离子水中加入放射性示踪剂混合液（包含Co-57、Mn-54及Zn-65）并添加定量生物炭开展实验，测定了pH、平衡时间以及基于朗缪尔（Langmuir）和弗罗因德利希（Freundlich）等温线模型的吸附容量等参数。采用高纯锗探测器（high-purity germanium detector，HPGe）通过γ能谱法对放射性示踪剂的活度进行定量分析。实验结果表明，在pH值为3.8、平衡时间30分钟的条件下吸附效果更佳。朗缪尔与弗罗因德利希等温线模型均能较好地拟合实验数据，且n值均大于1，证实了金属与生物炭之间存在吸附亲和性。Zn-65、Co-57及Mn-54的吸附容量分别为1.273 ng·g⁻¹、3.271 ng·g⁻¹及9.026 ng·g⁻¹。