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<p>The present study investigates the thermodynamic and kinetic behaviour of cadmium (Cd (II)) adsorption using a low-cost, eco-friendly silica adsorbent. Batch adsorption experiments were conducted using working solutions with concentrations ranging from 2.5 to 10&#xa0;mg/L. Maximum removal efficiency of 88% was achieved under optimized conditions: an initial concentration of 2.5&#xa0;mg/L, a contact time of 60&#xa0;min, pH 7, an agitation speed of 240&#xa0;rpm, and a temperature of 298&#xa0;K. Equilibrium data were analysed using linear and non-linear Langmuir and Freundlich isotherm models. While both models showed strong correlation in linear plots (R<sup>2</sup> = 0.994), the non-linear Freundlich isotherm exhibited the highest overall accuracy (R<sup>2</sup>= 0.999), suggesting adsorption on a heterogeneous surface. The maximum adsorption capacity (q<sub>max</sub>) was determined to be 0.428&#xa0;mg/g. Kinetic analysis revealed that the process best fits the pseudo-second-order model, with a non-linear correlation coefficient of R<sup>2</sup> = 0.9999 and a rate constant (k<sub>2</sub>) of 0.655&#xa0;g/mg/min. Thermodynamic parameters confirmed that the adsorption is spontaneous and exothermic, evidenced by negative Gibbs free energy (∆G<sup>0</sup> = -11.50&#xa0;kJ/mol at 298&#xa0;K) and negative enthalpy (∆H<sup>0</sup> = -137.48&#xa0;kJ/mol). The negative entropy (∆S<sup>0</sup> = -0.368&#xa0;kJ/K/mol) indicates a decrease in randomness at the adsorbent-solution interface during the process.</p>

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Study of Thermodynamic and Kinetic Behavior of Adsorption of Cd (II) on Silica Adsorbent”

  • 期刊论文

  • 发表日期：

    2026年5月27日

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  • Vivekanand Choudhary,
  • Twinkle Keshari,
  • Himanshu Shekhar

摘要

The present study investigates the thermodynamic and kinetic behaviour of cadmium (Cd (II)) adsorption using a low-cost, eco-friendly silica adsorbent. Batch adsorption experiments were conducted using working solutions with concentrations ranging from 2.5 to 10 mg/L. Maximum removal efficiency of 88% was achieved under optimized conditions: an initial concentration of 2.5 mg/L, a contact time of 60 min, pH 7, an agitation speed of 240 rpm, and a temperature of 298 K. Equilibrium data were analysed using linear and non-linear Langmuir and Freundlich isotherm models. While both models showed strong correlation in linear plots (R2 = 0.994), the non-linear Freundlich isotherm exhibited the highest overall accuracy (R2= 0.999), suggesting adsorption on a heterogeneous surface. The maximum adsorption capacity (qmax) was determined to be 0.428 mg/g. Kinetic analysis revealed that the process best fits the pseudo-second-order model, with a non-linear correlation coefficient of R2 = 0.9999 and a rate constant (k2) of 0.655 g/mg/min. Thermodynamic parameters confirmed that the adsorption is spontaneous and exothermic, evidenced by negative Gibbs free energy (∆G0 = -11.50 kJ/mol at 298 K) and negative enthalpy (∆H0 = -137.48 kJ/mol). The negative entropy (∆S0 = -0.368 kJ/K/mol) indicates a decrease in randomness at the adsorbent-solution interface during the process.