A New Adsorbent for Phosphorus Removal From Bark of Hibiscus syriacus Modified by Lanthanum

Based on the bark of Hibiscus syriacus, a new phosphorus adsorbent was modified by lanthanum chloride to remove phosphorus from wastewater. The mono-factor method was used to determine the optimal modification conditions of the adsorbent. The effects of pH, adsorbent amount, adsorption time and adsorption temperature were investigated. Results show that: (1) The optimal modification conditions of the bark of Hibiscus syriacus were the lanthanum chloride solution concentration of 7%, the calcination temperature of 300 ℃ and the roasting time of 2.5 hours. (2) When the initial concentration of phosphorus was 5 mg·L^-1, the solution acidity was pH 7 and the optimum dosage was 0.35 g, the best adsorption phosphorus removal rate reached to 94.99%. (3) When the adsorption time was 130 min, the adsorption reaction was in equilibrium. The adsorption modes of bark of Hibiscus syriacus modified by lanthanum chloride were all determined to the pseudo-second-order kinetic equation at different temperatures. (4) The Langmuir equation was suitable to describe the adsorption reaction which belonged to single molecule layer adsorption. At temperatures of 288, 298 and 308 K, the maximum adsorption capacity of modified bark of Hibiscus syriacus was 1.54, 1.55 and 1.63 mg·g^-1, respectively. (5) Adsorption thermodynamic analysis results show that the ΔG^θ, ΔH^θ and ΔS^θ was < 0, >0 and < 0, respectively, which means that the adsorption reaction was promoted when the temperature rose. These results also indicate that adsorption reaction using bark of Hibiscus syriacus modified by lanthanum chloride was a spontaneous, entropy increasing and endothermic process and belonged to the chemical adsorption. This study provides a theoretical reference for treating phosphorous wastewater by using bark of Hibiscus syriacus modified by lanthanum chloride.