ABSTRACT Two kinds of clinoptilolite-rich tuffs from the state of Sonora (Mexico), previously treated with NaCl solution and then modified with thiourea, were investigated to remove Cd2+ from aqueous solution in a fixed-bed column system. Experiments were conducted with a 30 mg L−1 Cd2+ solution at a pH value of 5 and three-bed heights of sodium- and thiourea-modified clinoptilolite-rich tuffs. The experimental data were examined with the bed depth service time model (BDST), the Thomas model, and a mass balance approach. According to the BDST model, the dynamic sorption capacity (No) for the thiourea-modified clinoptilolite-rich tuff was 0.0357 Kg L−1. This value corresponded to 1.2 times higher than that for sodium-modified clinoptilolite-rich tuff (0.0287 Kg L−1). The experimental data obtained for sodium- modified clinoptilolite-rich tuff (ZSGNa) with 3 cm of bed height, fitted to the Thomas model, with R2 = 0.9679 and Cd sorption capacity of 35.4 mg g−1, while for the thiourea-modified clinoptilolite-rich tuff (ZSGThio) with 4.5 cm of bed height, was 36.52 mg g−1 with R2 = 0.9368. The parameters calculated with the mass balance model describe a favourable process where the system with ZSGThio (6 cm bed height) had the best performance for sorption capacity up to the breakthrough point, qb = 22.35 mg g−1. The zeolite modified with thiourea exhibited higher capacity in Cd2+ removal than the one modified with NaCl, in the column with 6 cm of bed height. To investigate the mechanisms of removal of Cd2+ by the modified zeolites, Na⁺ was measured to determine the milliequivalents of cadmium removed. GRAPHICAL ABSTRACT

中文翻译：

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钠和硫脲改性的富斜发沸石凝灰岩从水溶液中吸收 Cd2+ 的固定床柱系统

摘要 研究了两种来自索诺拉州（墨西哥）的富含斜发沸石的凝灰岩，它们预先用 NaCl 溶液处理，然后用硫脲改性，以在固定床柱系统中去除水溶液中的 Cd2+。实验是在 pH 值为 5 的 30 mg L-1 Cd2+ 溶液和三床层高度的钠和硫脲改性的富含斜发沸石的凝灰岩中进行的。实验数据通过床层深度服务时间模型 (BDST)、Thomas 模型和质量平衡方法进行检查。根据 BDST 模型，硫脲改性的富含斜发沸石的凝灰岩的动态吸附容量 (No) 为 0.0357 Kg L-1。该值相当于钠改性的富含斜发沸石的凝灰岩 (0.0287 Kg L-1) 的 1.2 倍。床高 3 cm 的钠改性斜发沸石凝灰岩 (ZSGNa) 的实验数据符合 Thomas 模型，R2 = 0.9679，Cd 吸附容量为 35.4 mg g-1，而硫脲改性斜发沸石4.5 cm 床高的富凝灰岩 (ZSGThio) 为 36.52 mg g-1，R2 = 0.9368。使用质量平衡模型计算的参数描述了一个有利的过程，其中具有 ZSGThio（6 厘米床高）的系统在达到突破点 qb = 22.35 mg g-1 时具有最佳的吸附容量性能。在 6 cm 床高的柱子中，用硫脲改性的沸石比用 NaCl 改性的沸石表现出更高的 Cd2+ 去除能力。为了研究改性沸石去除 Cd2+ 的机制，测量 Na⁺ 以确定去除的镉的毫当量。