Studies On The Adsorption Of Magnetic Hydroxyapatite

As the economy develops, the industry grows rapidly. The environmental problemscaused by industrial water pollution became worse and worse, espccially heavy metals anddyes. The heavy metal ions can not be decomposed instead of aggregation in vivo. The dyewastewater contains large amounts of acid, alkali, organic matter. Which not only reduce thetransmittance of sunlight to decrease photosynthesis, but also do harm to human health, evencausing cancer or genetic mutations. Therefor, it is critical to handle heavy metal ion and dyes.Now, many researchers are looking for an inexpensive and efficient method to deal with theheavy metal ions and dyes that can not cause the secondary pollution. At present, the methodswhich are commonly used for the treatment of heavy metal ions and dyes are as flows:oxidation-reduction, electrolysis, chemical precipitation, ion exchange, adsorption and so on.One of the most widely used is adsorption.Hydroxyapatite of formula Ca10(PO4)6(OH)2, it is the main component of human andanimal bones, with a special crystal structure. It is a kind of adsorbent composed of inorganicmatter, which has a high adsorpton properties, biocompatibility, fixation of the metal ions anddyes, to used to treat metal ions and dyes in wastewater. Some improvements were madeabout hydroxyapatite. Make it magnetic, which is easy to be separated and recovered.In this paper, the magnetic hydroxyapatite adsorbent was prepared using the liquid-phasecoprecipitation. The adsorption properties of cobalt ion, Bright Green, Congo Red and DirectPink12B in aqueous solution were studied. The absorbance was determined byspectrophotometry, and then we obtain the adsorption capacity. We investigated the influenceof reaction time, temperature, initial concentration and pH value on the adsorption. Theoptimal adsorption conditions were determined. Meanwhile, kinetics and thermodynamics ofthe adsorption were also investigated. In Dynamics, it was found that the adsorption processof cobalt ion, Bright Green, Congo Red and Direct Pink12B were in line with thepseudo-second order kinetics equation, respectively, which can calculate the apparentactivation energy. In thermodynamics, the adsorption of cobalt ion onto the magnetic hydroxyapatite was fitted well with the Langmuir model. the adsorption of Bright Green,Congo Red and Direct Pink12B onto the magnetic hydroxyapatite was fitted well with theFreundlich model. In this way the adsorption equilibrium constant was obtained by fitting,and then the thermodynamic parameters for the adsorption process such as the changes ofGibbs free energy, enthalpy, and entropy were also obtained. The negative values of theGibbs free energe change indicates that the adsorption process is spontaneous.The study provides a theoretical basis for the wastewater treatment of heavy metal ionsand dyes.