Recycling agriculture wastes of ramie stalk as bioadsorbents for Cd2+ removal: a kinetic and thermodynamic study

In this study, we exhibit the recycling of agriculture wastes of ramie stalk as bioadsorbents for Cd2+ removal. Based on our experimental results, it is realized that Cd2+ adsorption to ramie stalk is highly pH sensitive, indicating the adsorption is driven by surface complexation reaction. The high adsorption capacity of ramie stalk toward Cd2+ (qm = 10.33 mg g−1, 0.09 mol-Cd g−1), which corresponds to around 21.95% of active adsorption sites available of ramie stalk, is believed to be closely related to its high cellulose and lignin content. The inhomogeneous surface of ramie stalk due to the high cellulose and lignin content also accounts for the observation that the adsorption kinetic is described well by the pseudo second order kinetic model. Results from thermodynamic studies suggest that the adsorption process is endothermic and spontaneous. All these properties demonstrate the potential of ramie stalk as a low cost bioadsorbent for the application of heavy metal removal.