Phosphorus adsorption characteristics of red soil in hilly region of South China

Red soil in southern hill region is an adsorbent with the characteristics of economy, accessibility and so on. The phosphorus adsorption characteristics of red soil were studied in this paper. Differences in parameters of phosphorus absorption at different concentrations with different weights of red soil were compared, and the influence of temperature and pH on the phosphorus adsorption was discussed. The results indicate that the isothermal adsorption data fit better with the Langmuir models than the Freundlich models. The saturated adsorption capacity of phosphorus can reach 0.454 mg/g when the temperature is 30°C, indicating that the red soil is a good adsorbent material for removing phosphorus, and can be well used as a medium in constructed wetland. The phosphorus adsorption quantity of red soil increases rapidly with time in the initial period and then approaches to a constant level in the later period. In the high concentration of initial phosphorus, the temperature on phosphorus adsorption of red soil is becoming apparent with the concentration increased. The tests show that the influence of pH at 6 to 9 on phosphorus adsorption is not significant. Hence, the influence of pH on phosphorus adsorption of red soil can be ignored in constructed wetland.