| Mineral processing wastewater, which is one of the main sources of heavy metal pollution, usually contains mercury, cadmium, arsenic, lead, copper, zinc and other heavy metals. As the mercury ion treated traditionally in mineral processing wastewater can hardly meet the discharge standard, we did a research on efficient mercury ion capture in this thesis. According to different discharge standards, the experiments were conducted in two stages, which were the fundamental processing that could meet the standards and the further processing in sequence.Fundamental processing was based on chelating precipitation, for which dithiocarbamate (DTCR-2),2,4,6-trimercaptotriazine(TMT-18B), Na2S and Ca(OH)2were chosen as the advanced treatment agents to remove low-level Hg2+from water. Due to its better treatment effect, DTCR-2was finally selected as the ideal agent. The influence of pH value, dosage of DTCR-2, reaction time, initial Hg2+concentration as well as other coexisting metal ions on the treatment conditions were studied. Results showed that the dosage of DTCR-2and initial Hg2+concentration had a greater impact on the capturing efficiency of DTCR-2for Hg2+. DTCR-2had high removal efficiency under the following conditions:100μg/L of initial Hg2+concentration, pH value of8.0,1.0times stoichiometric ratio of DTCR-2dosage and reaction time of10minutes. The residual Hg2+concentration of it was41.36μg/L which was below the national discharge standard (50μg/L). The dosage of DTCR-2should be increased accordingly to meet the discharge standard when dealing with mineral processing wastewater high in Hg2+concentration. Moreover, three heavy metal ions including Cd+, Pb2+and Cu2+, inhibited the capturing capacity of DTCR-2for Hg2+, and the inhibition effects of which ranked in the sequence of Cu2+>Pb2+>Cd2+, while Zn2+could promote the process. As a result, Cd2+, Pb2+and Cu2+should be removed preferentially in a process design for the actual mineral processing wastewater.Further processing was based on adsorption. Thiol-functional magnetic Fe3O4nanomaterials (Fe3O4@SiO2-SH) was prepared in laboratory by using magnetic iron oxide nanoparticle as the core, surface coating and functional modification, and then characterized by transmission electron microscopy (TEM) as well as fourier-transformed infrared spectroscopy (FTIR). In addition, the influence of pH value, initial Hg2+concentration and reaction time on the adsorption process and the adsorption mechanism of which were studied. Results showed that the magnetic nanomaterials prepared was dispersed well with an average diameter of20nm, and thiol functional groups were proved to be successfully grafted on the surface of magnetic nanomaterials. Moreover, thiol-functional magnetic Fe3O4nanomaterials could effectively absorb Hg2+with the maximum adsorption capacity of133.33mg/g. Adsorption efficiency was less affected by pH value, but greater impacted by the initial Hg2+concentration and reaction time. In addition, the adsorption behavior was well fitted with the Langmuir isotherm model and the pseudo-second-order kinetic model.On the basis of the above-mentioned theoretical research and practical projects, a preliminary design was conducted on the mineral processing wastewater treatment and reuse project in Henan. Through comparative study, the combination of physical and chemical methods, membrane and adsorption was selected as the core treatment process to ensure that the effluent could reach the class Ⅲ standards of "Surface Water Quality Standards", and83.3%of the wastewater could be reused for production simultaneously. Process was designed according to the discharge standard. And the reduced amount of heavy metals was accounted on the basis of expected treatment effects. The results showed that with the completion and running of this project, significant environmental benefits could be achieved. |
