The surface charge of the adsorbent 2-L ferrihydrite was calculated by the partial charge model for varying pH conditions. The value of the surface charge was used to predict the ability of the adsorbent to chemically adsorb and desorb the adsorbate. The crystal structure of the 2-L ferrihydrite material was regarded as two models: an exclusively octahedral model and a combined model comprising 20% tetrahedra and 80% octahedra. The partial charge model was used to calculate the surface charge of the adsorbent under varying pH conditions. In the exclusively octahedral model, the surface charge reached the highest value of +0.060 under acidic conditions, −0.088 in the neutral state, and the lowest value of −0.347 under alkaline conditions. In the case of the combined model, δ(OH) had the highest value of +0.056 under acidic conditions, −0.087 in the neutral state, and the lowest value of −0.332 under alkaline conditions. As a result, we confirmed that the surface charge of the adsorbent could have a positive value even in an acidic environment. That is, the surface charge of the adsorbent could become positive or negative according to the pH of the solution. In a solution in which the pH is below 10, the adsorbent could adsorb the negative phosphate because the δ(OH) would be positive. In contrast, in a solution with pH>10, the adsorbent could desorb the negative phosphate because the δ(OH) would be negative.

吸附剂 2-L 水铁矿的表面电荷通过不同 pH 条件下的部分电荷模型计算。表面电荷的值用于预测吸附剂化学吸附和解吸吸附物的能力。2-L 水铁矿材料的晶体结构被认为是两种模型：完全八面体模型和包含 20% 四面体和 80% 八面体的组合模型。部分电荷模型用于计算吸附剂在不同 pH 条件下的表面电荷。在纯八面体模型中，表面电荷在酸性条件下达到最高值+0.060，在中性状态下达到-0.088，在碱性条件下达到最低值-0.347。在组合模型的情况下，δ(OH) 在酸性条件下最高值为+0.056，在中性状态下为-0.087，在碱性条件下最低为-0.332。结果，我们证实吸附剂的表面电荷即使在酸性环境中也可能具有正值。也就是说，吸附剂的表面电荷可以根据溶液的pH值变为正电荷或负电荷。在 pH 值低于 10 的溶液中，吸附剂可以吸附负磷酸盐，因为δ (OH) 为正值。相反，在 pH>10 的溶液中，吸附剂可以解吸负磷酸盐，因为δ (OH) 为负值。