The Study Of Heavy Metal Pollution Produced By Leaching Tailings And Suppression Control

Ecosystem has been badly contaminated by heavy metals from tailings near Dabaoshan mine, Guang dong province. There has been no effective control method for heavy metal pollution in the mining area currently. In this paper, the tailings collected from Da Baoshan Mine are as research objects. Analysis of their composition and leaching expriments were conducted to study the release properties and kinetics of heavy metals. And in this paper, Triethylenetetramine, Montmorillonite and Triethylenetetramine-montmorillonite complexes are as inhibitors to inactivate heavy metals in the tailings. The impact of inhibitors on heavy metals was studied. The inhibitors and inhibitor-heavy metal complexes were tested by X-ray diffraction, infrared spectrum, thermo gravimetry, specific surface area analyzer and scaning electron microscope. And the reaction mechanism of the inhibitors was also researched in this paper. The conclusions are as follows:1. The tailings mainly have the elements of Fe, Si and Al. The content of S is very low. The main minerals in the tailings are quartz, lead alum, iron alum and gibbsite. The content of heavy metals in the tailings is high,which exist mainly in residue and sulfide. The tailings have a very low pH level.2. The pH of the leachates by leaching tailings with simulated acid rain ranged from 2.35~2.58, the conductivities of the leachates were high in the initial leaching stage and decreased gradually. Cu, Zn, Cd and Mn were similar in release progress, which could be divided into two stages, namely a fast leaching stage and a slow leaching stage. The release rate of Pb in the whole progress was relatively stable. The accumulative amount of heavy metals in the decreasing order was of Mn>Cu>Zn> Cd> Pb. With the pH of simulated acid rain decreasing, the pH of the leachates decreased, the conductivities of the leachates and the accumulative amount of heavy metals increased. The effect of the pH of simulated acid rain on the release of heavy metals in the decreasing order was of Pb>Mn> Zn> Cd >Cu. The leaching intensity of heavy metals in the decreasing order was of Mn >Cu > Cd > Zn > Pb . The kinetics of Cu, Zn, Cd and Mn could be properly described by Pseudo-second-order kinetic equation and Elovich equation, but the former was better. The kinetics of Pb could be properly described both by Two-constant equation and Pseudo-zero-order kinetic equation.3. Several tests of Triethylenetetramine-montmorillonite complexes indicated that Triethylenetetramine had inserted into the interlayer of montmorillonite. The suppression of Triethylenetetramine-montmorillonite complexes on the release of heavy metals was the best of three inhibitors. Triethylenetetramine-montmorillonite complexes could keep the ?suppression ratio of heavy metals high even if at pH3.0 or at the temperature of 40℃. The suppression ratio of heavy metals increased with the dosage of treatments increasing. The sorption of heavy metals on Triethylenetetramine-montmorillonite complexes and montmorillonite was rapid except the adsorption of Mn on Triethylenetetramine-montmorillonite complexes. The desorption amount of heavy metals on Triethylenetetramine-montmorillonite complexes was mostly lower than the desorption amount of heavy metals on montmorillonite except Cu.4. The adsorption of heavy metals on Triethylenetetramine-montmorillonite complexes fits Langmuir adsorption isotherm. The adsorption of Cu and Pb on montmorillonite fits Langmuir adsorption isotherm, but the adsorption of Zn, Cd and Mn fits Freundlich adsorption isotherm. The kinetics of the adsorption of heavy metals on Triethylenetetramine-montmorillonite complexes and montmorillonite can be properly described by Pseudo-first-order kinetic equation and Pseudo-second-order kinetic equation, but the latter is better. The tests of treatment-metal complexes indicated that adsorption happened between heavy metals and inhibitors.Besides adsorption, coordination reaction was produced by Hydroxyl or amino on the Triethylenetetramine-montmorillonite complexes and heavy metals.Triethylenetetramine-montmorillonite complexes have merits of both Triethylenetetramine and montmorillonite. Its suppression achieves the best results.