Abstract

In this study mixture of coconut shell and coir was used for Cr (VI) removal from synthetic wastewater and statistical tool Response Surface Modeling (RSM) was applied to optimize process parameters. The solution pH (2–6), reaction time (20–100 minutes) and adsorbent quantity (0.03–0.2 g) was optimized to find the maximum response of Cr (VI) removal using statistical Box-Behnken design (BBD) software. The equilibrium data obtained by the batch experiment were analyzed by ANOVA and found fitted in a second-order polynomial equation through multiple regression analysis. The optimum value of pH, adsorbent quantity and reaction time for 99% of Cr(VI) was found as 2, 0.1 g and 100 minutes, respectively. By using non-linear regression method it was found that Freundlich isotherm and Pseudo-second-order kinetic with high correlation coefficient (R²), low Chi-square (χ²) and root mean squares errors (RMSE), best describe the adsorption of Cr (VI) on mixture of coconut shell and coir (MCSC) surface. Positive enthalpy (ΔH°) and negative Gibbs free energy (ΔG^o) values confirm the endothermic and spontaneous nature of adsorption process. Pre and post adsorption phenomenon was confirmed by characterization of adsorbent using AFM, FTIR, SEM, and EDX analysis. The adsorbent MCSC has regenerative property and can be reused 3–4 times after treating with alkaline medium (0.2 N NaOH) and offered more than 60% removal of Cr (VI) at the fourth cycle. It can be inferred based on this study that MCSC is an effective adsorbent for Cr (VI) removal and can be used on an industrial scale for social and environmental benefit.

Novelty statement An agriculture waste mixture of coconut shell and coir (MCSC) without the addition of any chemical reagent, was used for Cr(VI) removal. As per literature survey and best of our knowledge, the adsorbent MCSC has not been reported for Cr (VI) removal. In the previous study, authors reported either coconut coir pith or coconut shell or coconut charcoal as adsorbent for Cr (VI) removal. The adsorbent MCSC is efficient even at very low doses (0.1 g) as compared to the reported adsorbent.

摘要

在这项研究中，椰子壳和椰壳纤维的混合物用于从合成废水中去除 Cr (VI) 和统计工具响应面建模（RSM) 用于优化工艺参数。使用统计 Box-Behnken 设计 (BBD) 软件优化溶液 pH (2–6)、反应时间 (20–100 分钟) 和吸附剂数量 (0.03–0.2 g) 以找到去除 Cr (VI) 的最大响应。批量实验得到的平衡数据进行方差分析，通过多元回归分析发现拟合在二阶多项式方程中。发现 99% Cr(VI) 的最佳 pH 值、吸附剂数量和反应时间分别为 2、0.1 g 和 100 分钟。通过非线性回归方法发现，Freundlich等温线和伪二级动力学具有高相关系数（R ²），低卡方（χ ²) 和均方根误差 (RMSE)，最好地描述了 Cr (VI) 在椰子壳和椰壳纤维 (MCSC) 表面的混合物上的吸附。正焓 (ΔH°) 和负吉布斯自由能 (ΔG ^o ) 值证实了吸附过程的吸热和自发性质。通过使用 AFM、FTIR、SEM 和 EDX 分析对吸附剂进行表征，确认了吸附前后现象。吸附剂 MCSC 具有再生性能，用碱性介质（0.2 N NaOH）处理后可重复使用 3-4 次，并在第四次循环中去除 60% 以上的 Cr（VI）。根据这项研究可以推断，MCSC 是一种有效的 Cr (VI) 去除吸附剂，可以在工业规模上用于社会和环境效益。

新颖性声明未添加任何化学试剂的椰子壳和椰壳纤维 (MCSC) 的农业废物混合物用于去除 Cr(VI)。根据文献调查和我们所知，还没有关于吸附剂 MCSC 去除 Cr (VI) 的报道。在之前的研究中，作者报道了椰子壳或椰子壳或椰子木炭作为去除 Cr (VI) 的吸附剂。与报道的吸附剂相比，吸附剂 MCSC 即使在非常低的剂量 (0.1 g) 下也是有效的。