Adsorption–desorption characteristics and pollution behavior of reactive X-3B red dye in four Chinese typical soils

Organic dyes have been turned into an important emerging type of chemical pollutants with the development of rural textiles, synthetic dye, printing, and dyeing industries and the continuous release from washing fabrics and clothes in recent decades. In order to assess ecological risk of reactive X-3B red dye as a typical dye, the adsorptive and desorptive traits of the dye in soils were investigated and the environmental factors influencing those processes were examined and discussed. Adsorptive and desorptive isotherms and dynamics of reactive X-3B red dye as a typical emerging pollutant were investigated by the standard batch experiments using four typical soils in China including relatively clean brown earth (burozem), drab soil (cinnamon soil), paddy soil (aquorizem), and red soil (krasnozem) and calculated by mathematical models using the Microsoft Excel software. It was suggested that the adsorptive behavior of reactive X-3B red dye by the four soils can basically be described using the Langmuir equation, and their maximum adsorbing capacity was in the sequence paddy soil > red soil > brown earth > drab soil. The adsorption could be divided into four stages including high-speed adsorption, slowdown adsorption, tardiness adsorption, and zero-approaching adsorption. It was also indicated that the adsorption ability of the dye decreased with the reduction in soil organic matter or air temperature and under neutral, runny, or unwatered conditions. The increase of desorption was observed with the decrease of soil organic matter and the increase of air temperature or soil moisture, while desorption was inhibited by the acidification or basification of soils. The comparative study validated that the basic adsorption–desorption laws of the dye at high concentrations were basically consistent with those at low concentrations. It could be concluded that reactive X-3B red dye has the potential properties of persistent organic pollutants with high ecological risk, and its release from contaminated soils and uptake by crops can be disturbed and changed by human activities.