Research On Removal Of Trivalent Antimony From Raw Water By Using Manganese Oxide Coated Sand (MOCS)

With the continuous development of China’s antimony industry,the use of antimony shows upward trend in our country. However, due to the mode of economic development in our country is still in transition,antimony industry basically still in the extensive non-sustainable development stages,so in recent years,antimony pollution problem in the water environment has become one of the more prominent heavy metal pollution problems. There are two main valence states of antimony which are trivalent antimony (Sb(Ⅲ)) and pentavalent antimony (Sb(Ⅴ)) exist in the aqueous environment, many studies have confirmed that the Sb(Ⅲ) is more than Sb(Ⅴ) in toxicity, solubility and mobility, so the research focus at home and abroad, mainly in the removal of Sb (Ⅲ) from industrial wastewater,while the adsorption is the most common method to remove antimony from wastewater. Manganese dioxide (MnO2) with its special surface physical and chemical properties become a kind of important adsorbent which can remove the toxic and harmful heavy metal ions from water. But in most studies MnO2exist in powder that is not easy to solid-liquid separation after the adsorption reaction. The MnO2for antimony concentration of wastewater is higher in a lot of research, and which of to combine it with the commonly used filter in water treatment such as quartz sand for the removal of trace antimony in raw water is rarely reported.The issue in both acidic and alkaline media conditions obtained Manganese Oxide Coated Sand (MOCS) and examined the load intensity of δ-MnO2on the surface of MOCS, the results showed that the surface manganese content of MOCS which is got at the acidic medium is much higher than the one which is got at the alkaline medium,and the charge number are0.73mg MnO2/gMOCS and0.11mg MnO2/gMOCS. SEM scanning results further confirmed the manganese load intensity of MOCS obtained in acidic medium higher than that prepared in alkaline medium, and the former’s MnO2surface coating is uniform and thick, appears as three-dimensional porous structure. The XRD detecting for the MOCS taken at acidic medium found the MnO2’s characteristic diffraction peaks in20=12.5°,24.7°,36.4°,which prove the crystal type of MnO2on MOCS’s surface is8-type indeed after compared it with the standard illustration. The MOCS’s FTIR testing showed that the absorption peak appears in the vicinity of the wave number of505cm-1,1081cm-1and1618cm-1, corresponding respectively to the Mn-0bond, Mn-OH surface hydroxyl groups and surface bound water.This issue studied the adsorption effect and adsorption mechanism of MOCS which is made at the acidic medium to the trace Sb(Ⅲ) in water through static testing, then examined some relevant factors that can impact the adsorption process that MOCS for Sb(Ⅲ). The experimental results showed that:①hile Sb(Ⅲ) initial concentration is100μg/L, pH=6.5, T=20℃and dosage of MOCS is30g/L, the removal rate of Sb(Ⅲ) can reached95.21%after6h contacting time;②osing3.0g MOCS in100mL solution which Sb(Ⅲ) initial concentration is100ug/L, under the condition of pH=6.5,T=20℃,the MOCS adsorbs Sb(Ⅲ) more than95%from the solution within the first60min, and after2h the adsorption process reaches a dynamic equilibrium;⑧The adsorption process of MOCS for Sb(Ⅲ) in water is in line with the Langmuir adsorption isotherm model,the correlation coefficient R2=0.9845,therefore the adsorption of MOCS for Sb(Ⅲ) in water is monolayer adsorption,and the theoretical adsorption capacity is76.53μg/g;④The adsorption dynamics of MOCS for Sb(Ⅲ) in water correspond to the quasi-second-order dynamics equation, the correlation coefficient R2=0.9961, and the quasi-second-order adsorption rate constant K2=0.0267g·μg-1·min-1;⑤The mechanism of MOCS remove Sb(Ⅲ) in water by adsorption is:Fixed on MOCS, the manganese of8-MnO2’s outer surface will coordinate with water molecules due to Mn’s coordination unsaturated, thus the H2O molecules dissociate and then form lots of surface hydroxyl groups. While Sb(Ⅲ) exist in water in the form of H2O·SbO(C4H4O6)-,so surface complexation reactions occurs between the surface hydroxyl groups and the H2O·SbO(C4H4O6)-, finally it is absorbed by MOCS then is removed from solution;⑥The pH value have a certain influence on removing Sb(Ⅲ) by MOCS, overall, the lower pH,the higer removal rate of Sb(Ⅲ).Because of the variation of pH value change the surface charge properties of δ-MnO2and then affect the complexation reactions to some extent between the surface hydroxyl groups and the Sb(Ⅲ); There is a certain influence on temperature for that adsorption reaction too, within a certain range,raising the temperature is conducive to the reaction. MOCS can ensure the removal rate of Sb(Ⅲ) to get up to95%in room temperature condition; The introduction of anion (NO3-,Cl-)will reduce the removal rate of MOCS for Sb(Ⅲ), and the anion concentration is higher, its influence is more remarkable, while importing cations (Ca2+,Mg2+)can promote the adsorption of MOCS for Sb(III).As a absorbent, MOCS has potential applications prospect at the dimension of the governance of antimony micro-polluted raw water.