Preparation And Property Studies On Recyclable Ditopic Ligand Extractants Which Simultaneously Extract Cation And Anions Of Metal Salts

Metal recovery via solvent extraction in hydrometallurgical process is essentially anion-exchange process in which the desired metal cation exchanges with protons from anextractant. However, the anions of the metal salt are not extracted and they may cause hazardto environment; large volume of organic solvents used during the solvent extraction processalso causes environmental issues. Similarly, cationic ion-exchange resins used for thetreatment of waste water containing heavy metal salts only absorb metal ions whereas theanionic ions still cause environmental pollution. To explore solutions to these problems, twoditopic ligands were prepared by reduction of their Schiff-base precursors with NaBHthe ditopic ligand was grafted onto Silica gel via covalent bond, thus enabling recycl4, ande and reuse of the solid extractants. The simultaneous binding of cation and anions of metal salts bythe silica gel supported extractants has been studied; and the extraction efficiency andselectivity analyzed; Experiments for recycling the solid extractants were carried out andextraction behavior of the recycled extractants was further studied. New methodology may beestablished from the research results for developing solid extractants which simultaneouslyand efficiently bind and transport cation and anions of heavy metal salts. The results willprovide theoretical foundation and technical support for solving the environmental problemsarised from the hydrometallurgical processes and the treatment of waste water containingheavy metal salts; and the research may also find application in the resource utilization ofheavy metal salt pollutants.The following researches have been performed:(1) Chemical modification has been carried out for silica gel in order to introduce functionalgroups of alkyl chloride and cap the residual silnol groups. The surface characteristic ofchemically modified silica gel was analyzed according to infrared spectroscopy and elementalanalysis.(2) 5-bromo-3-methylene morpholine salicylaldehyde and 5-methyl-3-methylene piperidinsalicylaldehyde were synthesized, and the compounds were characterized by NMR, IR andMS.(3) Salen-type Schiff bases containing a secondary amine backbone were prepared fromcondensation of above salicylaldehydes and diethylenetriamine. The Schiff-bases werereduced by NaBH4to afford saturated amine ligands thus improving their stability. The silicagel supported extractants D and E were obtained by grafting the ditopic ligands onto themodified silica gel.(4) The coordiation extraction property and selectivity of solid extractants towards cation andanion of metal salts have been studied by employing Atomic Absorption Spectrometry andIon Chromatography techniques. Solid extractant D was used as an example for conductingextraction/stripping and reusing behavior. The following conclusions were drawn from the experimental study: (1) Absorption equilibrium is established after shaking the mixture of extractant and metal salt in water for 2 hours at room temperature. Solid extractant D shows higher extraction efficiency than extractant E for simultaneous binding of cations and anions from metal salts.(2) Solid extractants D and E both exhibit highest extracting efficiency for of CuSO4 with extraction rate of 80-90% for Cu2+ and SO42-, while extractant D and E shows extraction rate of 50-80% for metal nitrate salts and other metal sulphates. The extractant D and E shows poor extraction for metal chloride salts (except CUCl2) with extraction rate 10-50%.(3) Competitive extraction experiments show that extractants D and E have good selectivity for Cu(II) over other metal ins while the selectivity for SO42-and NO3- are very similar; the extractants possess poor selectivity for Cl- ion.(4) Based on the extraction/stripping and recycling experiment as for CuSO4, the recovering efficiency for SO42- was 96.1% while further optimal trials are needed to improve the stripping efficiency for Cu(Ⅱ). Nevertheless, preliminary experiments reveal that the recycled extractant shows similar extraction efficiency as for the new extractant.