Optimizing adsorption of Pb(II) by modified litchi pericarp using the response surface methodology

• Chemically modified litchi pericarp was employed as a new adsorbent for removing Pb(II).
• Response surface methodology (RSM) was employed to optimize the adsorption parameters.
• Mechanisms of modified litchi pericarp for removing Pb(II) were discussed.

Litchi pericarp was chemically modified as a novel bioadsorbent (MLP) for Pb(II) adsorption in this study. Operating parameters such as contact time, adsorbent dosage, and initial pH of solution were investigated using batch assays and further optimized using response surface methodology (RSM). The results showed that the MLP exhibited a high adsorption efficiency of 99.97% for Pb(II), which was optimal at a contact time of 71.56 min, a initial pH of 6.81, and an adsorbent dose of 3.80 g/L. Adsorption processes of Pb(II) by MLP could be well described with Langmuir or Freundlich isotherms and a pseudo-second-order kinetic model. The maximum adsorption capacity of Pb(II) by MLP was determined as 163.93 mg/g, suggesting a highly promising potential for MLP to be used as a new bioadsorbent. Additionally, the thermodynamic study indicated that the adsorption process of Pb(II) by MLP was spontaneously and exothermic.