Research Mechanism Of Cr (â…¥) Adsorption From Aqueous Solution By CTMAB-Modified Phosphogypsum

Phosphogypsum is a solid waste which mainly comes from wet phosphoric acid production process, so is an industrial by-product. Chemical composition of phosphogypsum is quite complex. CaSO4·2H2O dominates a dominant position and also contains little phosphide and fluoride and other inorganics. With the amount of phosphogypsum increasing rapidly and annually produces about ten thousand tons for 4000-5000 in recent years. For a long time, resource way of phosphogypsum is mainly in four aspects of industrial applications, the application of the fertilizer industry, the construction industry applications, and agricultural applications. But the utilization of phosphogypsum is low and has not yet reached 15%. Stockpiling a lot of phosphogypsum caused an extremely negative impact on the environment to a certain extent. Stockpiling of phosphogypsum is not only accounted for a lot of land resources but also to cause secondary pollution easily. Therefore, utilization of phosphogypsum can have a positive impact on society and the environment.Chromium-containing wastewater is a more common form in heavy metals waste water which is mainly from industrial production, especially in the electroplating industry. Chromium is internationally recognized as one of the three heavy metal carcinogens and has also been listed as one of 129 kinds of major pollutants US Environmental Protection Agency. Common valence state of chromium is trivalent chromium and hexavalent chromium, toxicity of hexavalent chromium is 500 times than trivalent chromium. Hexavalent chromium is easy for the body to produce carcinogenic and teratogenic effects. With the rapid development of industry, hexavalent chromium caused serious environmental pollution as an important source of environmental pollution. For the reason, effective treatment of hexavalent chromium contamination is one of the issues that must be addressed in the field of environmental protection.Currently in the field of wastewater treatment, Adsorption method has the advantages of low cost and good effect compared to other treatment processes. However, due to some material such as activated carbon is expensive so that absolute costs is higher, tus affecting a wide range of promotional use. In the current research field, how to effectively develop a adsorbent that is low cost, wide range of sources has become a critical hotspot.This paper make phosphogypsum as a sorbent matrix, to modify phosphogypsum by adding surfactant. To deal with chromium-containing wastewater by modified phosphogypsum is effectively and low cost and easy to operate. This paper systematically studied the preparation process of the new adsorbent of phosphogypsum and the adsorption mechanism of chromium-containing wastewater.The study has shown that effect of organically modified phosphogypsum by surfactant of cetyl trimethyl ammonium bromide is better than inorganic modified phosphogypsum by acid and alkali. Best dosage of cetyl trimethyl ammonium bromide to modify phosphogypsum is 1.5g/L, highest removal percentage is 88%.Through characterization analysis of modified phosphogypsum, the surface and interlayer of phosphogypsum is filled with cation. The adsorption mechanism is the cation occurs electrostatic adsorption with HCrO4、CrO42- and CrO72- so that hexavalent chromium is removed. Optimum adsorption conditions is as follows:when the pH is 2-6, adsorption time is 70min, the initial concentration of heavy metal ions is 40mg/L-50 mg/L, adsorption dosage is 0.2g/100mL, adsorption temperature is 25 ℃, the maximum adsorption capacity of hexavalent chromium by modified phosphogypsum is 16.3225mg/g. Through analysising the response surface methodology, we can see that pH has significant effect on adsorption process. The exist form of hexavalent chromium is decided by pH of the aqueous solutions, so pH is decisive factor in the adsorption process.The results indicates that the adsorption results fit both in the Langmuir and the Freundlich model, however, the Langmuir equation could describe the adsorption results better. The ability of adsorption hexavalent chromium by modified phosphogypsum is strong. The initial stage of adsorption ccould be mirrored with the Lagergren pseudo-first-order kinetics, Lagergren pseudo-second-order kinetics, Elovich adsorption equation and intra-particle diffusion model. The absorption of hexavalent chromium onto modified phosphogypusum keeps in accordance with Lagergren pseudo-second-order kinetics in the entire adsorption stage. The absorption behaviors of hexavalent chromium on modified phosphogypusum are controlled by the common effect of physical adsorption and chemical adsorption. The results of adsorption thermodynamics indicate that the adsorption of the hexavalent chromium onto modified phosphogypusum is endothermic process. The spontaneous of adsorption is enhanced with temperature increases. Desorption experiments showed that adhesion power of Cr (VI) in CTMAB-phosphogypusum was strong.The results of studies showed that it is possible to make phosphogypusum to be a better adsorbent with cetyl trimethyl ammonium bromide. It is promising to remove hexavalent chromium from aqueous solutions using the adsorbent. At the same time, it provides a new way of thinking for utilization of phosphogypsum.