Calcined Hydrotalcites For The Selective Adsorption Of Sulfur Anion

Thiosulfate and thiocyanate co-exist in many wastewater, such as coking wastewater, photographic, printing photos processing wastewater, printing and dyeing wastewater, plating wastewater and mining wastewater. These sulfur compounds are major pollutants in wastewater. Thiosulfate is biological nutrients, could easily lead to eutrophication, the thiocyanate is toxic to biological effect, if they were directly discharged into water, human and aquatic life will be in danger.Layered Double Hydroxides, abbreviated as LDHs; also known as hydrotalcite-like material, are a class of layered inorganic materials, they show unique charm in the adsorption of anions and organic molecules, for their special property such as "structural memory " effect,exchangeable interlayer anions,large specific surface area and other excellent properties. In this paper, to separate the thiosulfate and thiocyanate in water, we use calcined hydrotalcite (CLDH or LDO) as adsorbent, selectively adsorpted thiosulfate in water. The Mg3Al-CO3-LDH were prepared using separate nucleation and aging steps, we calcined the LDH to get LDO. Through adsorption experiments, we found that thiosulfate were adsorbed by LDO preferentially in the mixed solution, the initial molar concentration of thiosulfate and thiocyanate can be down from 1:1 to 1:7. In the adsorption process, thiosulfate adsorption kinetics and adsorption thermodynamics were studied, the adsorption of thiosulfate thermodynamically consistent with Langmuir model; The pseudo-second order kinetics model can be used to describe the uptake process. The value of Ea was calculated to be 75.898 kJ/mol. Our results suggest that the process of thiosulfate uptaking was controlled by the reaction rate of thiosulfate with the CLDH rather than diffusion. After the adsorption reaction, LDO adsorbed S2O32-formed hydrotalcite with a new structure. Through the study of S2O32--LDHs in aqueous solutions we found that the S element were released slowly from the layers of LDHs, wich could last about 15 days, more than half of S was released from the layers. we can conclude S2O32-LDHs could be used as a new S-release fertilizer in agriculture.