Several conventional techniques for heavy metals decontamination for instance ion exchange, evaporation, precipitation and electroplating have been utilized in preceding years. Though these techniques have some drawbacks, adsorption using low-cost biosorbents is environmentally friendly. In this study, the potential of several natural and agricultural wastes as economical biosorbents for the reduction of Cr(VI) ions from polluted water has been reviewed. The application of adsorption models, as well as the impact of adsorption factors on heavy metals eradication, has been considered in this review. The study revealed that efficient reduction of Cr(VI) from water and wastewaters is highly dependent on the pH of the solution, shaking time, adsorbent type, initial concentration and temperature. The review of the relevant literature indicates that the maximum removal efficiency of Cr(VI) using the various low-cost adsorbents ranged from 50.0–100.0% with optimum pH and contact time ranging from 2.0–6.0 and 30.0–180.0 min, respectively at room temperature (25.0 °C). Furthermore, considering all the studies reviewed, the pseudo-second-kinetics and Langmuir isotherm are the dominant models that best described the Cr(VI) equilibrium data. The thermodynamic parameters suggested that the biosorption of Cr(VI) on the biosorbents was spontaneous, realistic and endothermic at the temperature range of 30.0–45.0 °C. It is found that the natural and agricultural wastes as cheap biosorbents are feasible replacements to commercial activated carbons for metal-contaminated water treatment. However, gaps have been identified to improve applicability, regeneration, reuse and safe discarding of the laden adsorbents, optimization and commercialization of suitable agricultural adsorbents.

前几年已经使用了几种用于重金属净化的常规技术，例如离子交换、蒸发、沉淀和电镀。尽管这些技术有一些缺点，但使用低成本的生物吸附剂进行吸附是环境友好的。在这项研究中，回顾了几种天然和农业废物作为经济生物吸附剂减少污染水中 Cr(VI) 离子的潜力。本综述考虑了吸附模型的应用以及吸附因子对重金属根除的影响。该研究表明，有效减少水和废水中的 Cr(VI) 很大程度上取决于溶液的 pH 值、振荡时间、吸附剂类型、初始浓度和温度。丙）。此外，考虑到所有审查过的研究，伪第二动力学和 Langmuir 等温线是最能描述 Cr(VI) 平衡数据的主要模型。热力学参数表明，在 30.0-45.0° C的温度范围内，Cr(VI) 在生物吸附剂上的生物吸附是自发的、真实的和吸热的。研究发现，作为廉价生物吸附剂的天然和农业废物是用于金属污染水处理的商业活性炭的可行替代品。然而，在提高负载吸附剂的适用性、再生、再利用和安全丢弃、合适的农业吸附剂的优化和商业化方面，已经发现了一些差距。