Jovanovic and Sips Isotherm Parameters of Mango Seed Shell Cadmium Ion Sorption from Aqueous Solution

Abstract

Cadmium (Cd) is not crucial for animal and plant life, and its total elimination from irrigation or drinking water supplies will not deprive water consumers of any beneficial nutrient. Its toxicity to humans has been reiterated, and several mechanisms to get rid of it via numerous adsorbents have been researched over several decades, without capturing mango seed shell (MSS) adsorption data performance under the 2-parameter Jovanovic and the 3-parameter Sips isotherm models. The present study tries to address those gaps. As such, the parameter values, q_max = 97.51 mg/g and KJ = -0.0202 L/mg for Jovanovic, and K_s = 20.42 L/g, β_s = 1.16, and a_s = -0.046 L/g for the Sips model, were computed and obtained. After a series of fine-tuning steps to improve model fitting and achieve greater convergence, it led to an R² value of 0.7231 and 0.9998, respectively. In addition to error functions, residuals and chi-squares were evaluated, it was found that the Jovanovic equation couldn’t describe Cd(II) uptake by MSS, due to its larger return of statistical metric values compared to Sips. Therefore, an existing Cd²⁺-MSS dataset favouring the Langmuir model as the best was re-evaluated—which then pinpoints the Sips isotherm as the best (in this study) at a low % difference of 0.04-20.59% for predicted vs. observed equilibrium Cd²⁺ uptake (q_e). The adsorption mechanism of Cd(II) onto MSS described by Sips is favorable and efficient adsorption, where the heterogeneous MSS surface has a high affinity for Cd²⁺ at low concentrations. A huge research gap still exists, as Jovanovic and Sips isotherm models are less commonly assessed during adsorption studies. For sustained water purification using MSS as an adsorbent, its abundance must be taken into consideration.