Study On The Deep Removal Of Heavy Metal Ions In High-salt Waste Water

With the rapid development of the industrial economy,water pollution has become increasingly serious.For the purpose of environmental protection and water reuse,the technology of deep-removing heavy metal ions in wastewater is a major current hotspot.In this paper,the removal of low-concentration heavy metal ions in high-salt coal-to-oil wastewater after electrodialysis was studied.The removal effect of heavy metal ions in high-salt wastewater was investigated using NF90-2540,2540-TS80-TSF and DL2540nanofiltration membranes.It can provide experimental basis for nanofiltration technology to remove low concentration heavy metal wastewater.Firstly,the effects of pH,transmembrane pressure difference and feed pump frequency on the retention effect of heavy metal ions were studied on NF90-2540 and 2540-TS80-TSF nanofiltration membranes.The results showed that:The effect of treating heavy metal ions with low concentration is very good,and the content of heavy metal ions in the produced water can meet the first-grade standard for comprehensive wastewater discharge.The optimal conditions of NF90-2540 nanofiltration membrane treatment of high-salt coal-to-oil wastewater is pH 5.16,feed pump frequency 16 Hz and transmembrane pressure difference of 2.5 MPa;The optimal conditions of 2540-TS80-TSF nanofiltration membrane treatment of high-salt coal-to-oil wastewater is pH 5.1,a feed pump frequency of 14 Hz and a transmembrane pressure difference of 2.5 MPa.However,the permeation fluxes of the two nanofiltration membranes increase with the recovery rate of the produced water,and the attenuation phenomenon is serious.Therefore,heavy metal ions in the high-salt wastewater cannot be efficiently removed.The DL2540 nanofiltration membrane has a high permeation flux.However,the nanofiltration membrane has poor effect on the retention of heavy metal ions at low concentration,and can not achieve the purpose of deep removal of heavy metal ions.The complexation of heavy metal ions with complexing agents was investigated.The heavy metal ions in high-salt wastewater were deeply treated by the complex nanofiltration process.The experimental results show that the addition of complexing agents can significantly improve the performance of nanofiltration membranes for trapping heavy metal ions.Disodium ethylenediaminetetraacetate?EDTA?has a significant effect.Design-Export software based on response surface methodology?RSM?was used to optimize the complex nanofiltration process.The results showed that DL2540 has the best interception of heavy metal ions under the conditions of M_?????:M_?EDTA?=3.42:1?feed flow rate=12.42 Hz?transmembrane pressure=1.92 MPa and pH=3.06.When the recovery rate is 77%,the concentration of Pb²⁺is 0.49 mg�L^-1,and the concentration of Cd²⁺is 0.09mg�L^-1,which can meet the first-grade standard for comprehensive wastewater discharge.When the pH of concentrated water with the enriched heavy metals is adjusted to 12,heavy metal ions are precipitated and removed,and the treated waste water is returned to the feed tank for circulation treatment,thereby achieving high-efficiency and deep-removal of high-salt coal chemical wastewater.