Study On The Removal Of Heavy Metal Ions By Materials With Super Adsorption Performance Prepared From Andradite Minerals

With the increase of human standard living and rapid development of industry,the problem that of heavy metal ions pollution in water environment has seriously threaten our ecological environment,there are some common heavy metal ions such as Pb²⁺、Cr（Ⅵ）、Hg²⁺、As（Ⅲ）and so on.It is difficult to remove the heavy metal ions of low concentration in waterbody and heavy metal ions themselves are not biodegradable,the problem troubles us for a long time.This study was designed from the point of iron-based adsorption for heavy metal materials for the problem that most iron-based materials had a low selectivity and harsh implication environment.The Fe element was activited in andradite using certain modification method to prepared iron-based heavy metal adsorbent with high selectivity and high adsorption capacity.The research systematacially studied the adsorption behavior of composite adsorbent for heavy metal ions(Pb²⁺、Cr（Ⅵ）、Hg²⁺)in solution,which revealed the removal mechanism of heavy metal ions by analysing morphology and structure on composites.It includes the following contents:（1）The main elements in andradite are Si、Ca、O and Fe and the like by analysing the crystal chemistry of Tongling tailings,and the Fe element mainly occurs inertial silicate minerals.Therefore,we used oxalic acid dihydrate to activited Fe element in andradite utilizing the theory of solid-state phase transformation by one-point pyrolysis method and the ferrous oxalate was further synthesized on the surface of andradite,then a new andradite-based composite adsorbent.（2）The mechanism of Pb²⁺removal in solution was further studied because of amounts of oxygen-containning founctional groups and complexation of oxalate.The composites had a high adsorption capacity of 862.07 mg/g for Pb²⁺removal,which were much higher than most of other adsorbents,such as iron-based materials and biologic materials.The main contributor for Pb²⁺removal was ion exchange,The ion exchange occurred between Pb²⁺in solution and Ca²⁺in calcium oxalate generating insoluble lead oxalate precipitation,the complexation and electrostatic attraction also involved.The fitting process for Pb²⁺removal accorded with second-order dynamic model and Langmuir model.（3）On account of iron-reduction state in composites,the composite was applied on removal of highly toxic Cr（Ⅵ）that was reducted to hypotoxic Cr（Ⅲ）.The composite materials belong to andradite-based nano ferrous oxalate structures,the diameter of spherical ferrous oxalate was2.97 nm and the specific surface was 18.26 m²/g.The results of study showed that the composite materials could be applied on a condition of wide p H value,which overcame the boundedness that most of iron-based materials for Cr（Ⅵ）remvoal could not be used in a wide p H value in solution.The redox precipitation played a major role in mechanism of Cr（Ⅵ）remvoal,surface complexation and electrastatic attraction also worked.The research of this paper not only carved a new path for the comprehensive utilization of iron-rich garnet secondary resource but also laid the foundation for heavy metal recovery techniques.