This article describes how selectively anionic organic molecules could be removed from aqueous medium using naturally available gypsum (GS) adsorbent. Gypsum (CaSO₄.2H₂O) shows strong interactions with anionic dye molecules while it dos not show any affinity towards cationic dye molecules. We have shown the removal efficiency of gypsum taking chlorazole yellow (anionic dye) and methylene blue (cationic dye) as examples of adsorbates. The GS has been to be even more effective than activated carbon in attaining chlorazole yellow (CY) removal. Three well-known kinetic equations e.g. pseudo-first-order, pseudo-second order and intraparticle diffusion were exploited to interpret the experimental data. Results show best fitting with second order kinetic process with excellent regression coefficient (r² = 0.99) for the adsorption process. The equilibrium data were analyzed exploiting some adsorption isotherm models. It was apparent that the Freundlich isotherm model superbly fitted for CY dye adsorption process. And the maximum adsorption capacity, Q_m, was obtained as 12.85 mg g⁻¹ at room temperature. The negative values of Gibb’s free energy change (ΔG^o) suggests that the CY dye molecule adsorption process is spontaneous in nature. Moreover, negative enthalpy change (ΔH^o) indicates the exothermic nature of the adsorption process. The outcome could be exploited where anionic organic molecules are required to be separated, selectively.

本文介绍了如何使用天然可用的石膏（GS）吸附剂从水性介质中选择性去除阴离子有机分子。石膏（CaSO ₄ .2H ₂O）显示出与阴离子染料分子的强相互作用，而没有显示出对阳离子染料分子的任何亲和力。我们已经显示了以氯唑黄（阴离子染料）和亚甲基蓝（阳离子染料）为吸附质的石膏的去除效率。GS在去除氯唑黄（CY）方面比活性炭更有效。利用三个著名的动力学方程，如拟一阶，拟二阶和粒子内扩散来解释实验数据。结果表明，二阶动力学过程具有最佳的回归系数（r ² = 0.99）。利用一些吸附等温线模型分析了平衡数据。显然，Freundlich等温模型非常适合CY染料吸附过程。并且在室温下获得最大吸附容量Q _m为12.85 mg g ^-1。Gibb自由能变化的负值（ΔG ^o）表明CY染料分子的吸附过程是自然发生的。此外，负焓变（ΔH ^o）表示吸附过程的放热性质。当需要选择性地分离阴离子有机分子时，可以利用该结果。