Research On Application Of Heavy Metal Capturing Agents In Low-concentration Mine Wastewater Treatment

In recent years, with the development of social economy, the human are developing mineral resources of Poyang lake basin in an unprecedented scale. A lot of mine wastewater discharge into Poyang lake basin, as a result heavy metal pollution of Poyang lake basin is becoming more and more serious, posing a threat to human society and ecological environment security. So in order to actively respond to the state council issued the "twelfth five-year" plan in2011year for the prevention and control of heavy metal pollution, therefore looking for a simple and cost-effective method for further deep processing low concentration of mine wastewater is of great significance.Heavy metal capturing agent method has many virtues contrasting with many other treatment methods, such as high reaction efficiency,high settling speed of the sludge low moisture contents residue stability、no secondary pollution and good selectivity and so on, especially for low content heavy metal wastewater, handling costs are relatively lower, thus it becomes the focus of heavy metal processing research in the domestic and overseas.There are a variety of heavy metal capturing agents on the market at present, and study on treating wastewater containing a single kind of heavy metal ion by heavy metal capturing agent are payed more attention, but for treating the coexistence of a variety of heavy metal ions of mine wastewater has no system analysis and evaluation on some aspects such as efficiency and economy. Therefore, in this paper, a variety of heavy metal capturing agents like DTCR-2, CM-1, LQ220H, TMT and PMT are selected to remove Cu2+, Pb2+, Zn2+, Cd2+and Cr3+of low concentration mine wastewater. The main research contents and conclusions are as follows:(1)By comparing treatment efficiency and economic cost of these heavy metal capturing agents, preliminary screen the better capturing agent that fit for treating low concentration of mine wastewater. Results show that under the same treating conditions, except LQ220H can’t meet the expected target, the remaining four can effectively deal with heavy metal ions. DTCR-2has higher and stabler removal rate, moreover it has the lowest treatment cost(1.38RMB per ton waste water); while TMT has the highest removal effect, large precipitation particlesp, has better selectivity in Zn2+, Pb2+and Cd2+, and is easy to storage and transport. So preliminary select DTCR-2and TMT as the better capturing agents in low concentration of mine wastewater treatment.(2)Five kinds of trapping agents and each capturing products are analyzed through ultraviolet spectrum, infrared spectrum scanning and X ray diffraction characterization, ultraviolet spectrum scanning analysis results show that DTCR-2and CM-1have the same functional group, they both are dithiocarbamate salts, as well as LQ220H、TMT and PMT have the same functional group which is N=C-S; infrared spectrum analysis results show that DTCR-2and CM-1molecule contain C-S single bond and C=S double bond, even N-CSS-bond, which is further evidence that this two kinds of capturing agents belong to dithiocarbamate salts. LQ220H, TMT and PMT molecules contain triazine ring, all belong to trimercaptotriazine salts. And the IFR analysis results of the capturing products show that the heavy metal ions combine with five kinds of heavy metal capturing agents, which all belong to the chelation; X-ray diffraction analysis results further show that DTCR-2and CM-1belong to dithiocarbamate salts, with the crystallinity of77.37%and79.47%respectively. LQ220H、TMT and PMT belong to the same class, with the crystallinity of83.56%,85.98%and81.09%in turn, and TMT has the biggest crystallinity and strongest diffraction peak intensity. Capturing agents’ crystallinity reduce after chelating with heavy metals, DTCR-2、CM-1、LQ220H、TMT and PMT capturing products’ crystallinity become58.47%,61.23%,68.13%,71.96%and71.90%in turn. Crystallinity of DTCR-2is lower than LQ220H, while the capturing effect is obviously better than that of LQ220H, which shows the chelation between heavy metal ions and capturing agent not only occurs in the crystalline region, also occurs in the amorphous area. The characterization analysis results ensure that further selecting DTCR-2and TMT for subsequent research in processing mine wastewater from structure.(3)DTCR-2and TMT were used to deal with the mining waste water, and it turns out that the best operating conditions of DTCR-2for low concentration of mine wastewater treatment are pH value controlled in8, adding amount of1%capturing agent1.2mL, stirring at room temperature for5minutes, adding combined flocculant 100mg/L PAC and5mg/L PAM, total reaction time of15minutes; and the best operating conditions of TMT are pH value controlled in7, adding amount of10%capturing agent0.4mL, stirring at room temperature for5minutes, adding combined flocculant100mg/L PAC and5mg/L PAM, total reaction time of20minutes; the maximum leaching amount or in different pH conditions of Cu2+、Zn2+、Cd2+、Pb2+and Cr3+from DTCR-2and TMT capturing product are far below the leaching amount of the sediment of NaOH precipitate, therefore, when DTCR-2and TMT capturing products were in landfill, the leaching amount of heavy metals to the environment is much lower than alkali precipitate, which greatly reducing products’ secondary environmental pollution risk. In addition, the stability of TMT capturing product was stronger than DTCR-2’s, consequently with better application prospect in the aspect of heavy metal wastewater treatment.(4)The capture principles of DTCR-2and TMT combination with heavy metal ions were researched, the results indicate that effective sulfur composition content of the two kinds of capturing agents was high, clannishness phenomenon was much obvious, aggregation degree was high, which was contributed to precipitating after capturing heavy metal ions, therefore their efficiencies were good; After chelation with heavy metal ions, the pellet surface gap were stuffing and their structures become more tightly sealed, which can be thought of DTCR-2and TMT dealing with heavy metal wastewater treatment process with the electrical neutralization, rock bridge, three kinds of mechanism. Through element analysis deduces the C:H:N:S ratio of DTCR-2material is3:6:1:2, which determine the DTCR-2structure contains a disulfide generation amino functional groups, the C:H:N:S ratio of TMT material is5:15:3:3, proving that the structure of TMT functional groups contains triazine ring. DTCR-2and TMT have good efficiency in mine wastewater treatment, and the capture mechanism are similar, that of heavy metal ions combine heavy metal ligand atoms S on the capture agent, and S atom and heavy metal is easy to form covalent significant coordination bond, hence the capture product stability is good and the secondary pollution risk is low.