Phosphate Rocks Activated With Organic Acids And Its Effect On Copper Removal In Aqueous Solution

Three medium-grade PRs were selected from Hubei province, experiments with several common low molecular weight organic acids (Low molecular weight organic acids, LMWOAs) and inorganic acid (hydrochloric acid, sulfuric acid) were carrie out. And comparison of the activation effectiveness between the acids was analyzised. The different effects of phosphorus(P) release, such as the concentration of organic acids, activation time, activation temperature, pH, acid ion, liquid-solid ratio, particle size of PR, on PRs were investigated. At the same time, the calcium (Ca) and magnesium (Mg) release were determined. The morden techniques, such as infrared spectroscopy (IR), Raman spectroscopy (Raman), X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and X-ray photoelectron spectroscopy (XPS) were used to investigate the mechanism between oxalic acid and PR. In this paper, the Cu2+removal from aqueous solution with PR and activated phosphate rock (APR) and its influencing factors were also investigated. The techniques of Raman, XRD and XPS were applied to analysis the reaction between Cu2+and PR (as well as APRs). The main results are as follows:(1) The results of PRs dissolution in the presence of acids showed that:inorganic acids and organic acids can activate the PRs, but the effects of P release from PRs vary different acids. In laboratory experiment, as the acids concentrations are ranged from0.10to0.50mol/L, the P release from PRs is as follows:sulfuric acid> oxalic acid> hydrochloric acid> citric acid> tartaric acid> formic acid> malic acid> succinic acid> acetic acid. In terms of the same type of organic acid, the effectiveness of the acids on the P release is as this order: oxalic acid> tartaric acid> malic acid> succinic acid, and formic acid> acetic acid. The results indicate that acids would activate the PRs, and the more th amount of P release are, the more the stronger the acids are. If the acidity of the LMWOAs are the similar, their activation effect on PRs are as follows:ternary-acid> dicarboxylic-acid> mono-acid. The effectiveness of mixed acids is not stronger than that of single acid(2) The amount of P release is related to various factors. In terms of oxalic acid and citric acid, the results that the results of effects on PRs activation show that:the higher the concentration of acids were, the better the activation effectiveness were; there was a better negative correlation between the pH and the amount of phosphorus release from PRs. The higher the ratios of liquid-solid (volume of acid solution to amss of PR) were, the smaller the particle size of PR was, the more the phosphorus content of PR was, the more the P release from PR was.(3) The amount of P release from PRs is related to the acids concentration and reaction time. The processes of PRs dissolution were described with different kinetic equations. When the concentrations of oxalic acid and citric acid were0.50mol/L, the amount of P release from PRs increased with time. Within24hours, the rate of P release was rapid, and the firrst-order equation would be described the tendency. After6days, the P release rate further slowed down, and the Elovich equation would be stated the next process. When the concentration of oxalic acid and citric acid was20mmol/L, the P release from PRs was shown a decreasing trend. The P release processes of BKPR and NZPR would be described with linear equation, and ZXPR with Elovich equation.(4) The Ca2+and Mg2+release from PRs was also accompanied with the process of P release, but there were differences in Ca2+and Mg2+release from PRs. While the concentration of oxalic acid and citric acid was0.10-0.50mol/L, the amount of Ca2+release were significantly different in concentrations; while the Mg2+release was no difference. While the concentrations of oxalic acid and citric acid were0.010-0.050mol/L, the results were on the contrary.(5) The effects of organic acids ion P release from PRs varied. When the concentration of oxalate increased, the difference of P release between various concentrations of acid ion were significant difference (p<0.01), but the difference of citrate was not significant (p>0.1). When the pH of solution was controlled, the P release increased with the acid ion concentration increasing, there were significantly different in P release between different concentrations.(6) The spectra of FTIR, XRD, Raman, SEM/EDS and XPS of the tested samples indicated that there were obviously significant differences between PRs and activated PRs. And the results stated that when the PRs reacted with oxalic acid and citric acid, some new substances calcium oxalate monohydrate and calcium hydrogen phosphate dihyrate in oxalic aicd, and only new material, calcium dihydrogen phosphate monohyrate, was in presence of citric acid.(7) The PR and APR could be a new passivating agent to remove the heavy metals Cu2+ in aqueous solution. The effectiveness of Cu2+removal with PR and APR was related with the pH of the solution. When pH ws ranged from3-5, the amount of Cu2+fixed in minerals gradually increased with pH increasing. Adsorption isotherm equation showed that the Freundlich equation could be better described the adsorption reaction, and the temperature was conducive to Cu2+removal. The ionic strength of the medium and other co-existed heavy metal Cd2+could influence Cu2+removal with PRs and APRs. With the increase in ionic strength decrease and the concentration of Cd2+ions increase, the amount of Cu2+removal decreased. There was competition and collaboration between the Cd2+and Cu2+. The amount of Cu2+adsorbed in APR was more than that of PR.(8) When the PR and APR were added into the Cu2+solution, the Cu2+adsorption occurred in the surface of PR and APR. The results of FTIR, Raman, XRD and XPS showed that the new copper salts were not found in the surface of PR and APR; there was mainly physical adsorption between the Cu2+and PR (APR), maybe was chemical adsorption.