Preparation Of Novel Chelating Sponge As Adsorbent For Fast Removal Of Ni²⁺ And Cd²⁺ From Water

Many water pollution accidents occurred in China every year, and these accidents not only destroyed the ecological environment, but also cause enormous economic loss. Compared with ordinary water pollution, heavy metal pollution accidents could cause more damages because of uncertain characteristics. Once the pollutants enter the water, it could spread rapidly and caused a wider range of environment damage. On the other hand, due to development of mining, metallurgy and related industries, ordinary heavy metal water pollution is a growing and urgent problem. And absence of regulation aggravated the problem more seriously. The current disposition technology of heavy metal water pollution accidents included coagulation/precipitation, chemical oxidation/degradation and activated carbon adsorption. However, there were some deficiencies in the actual application process。In this paper, a new spongy adsorbent was prepared for fast removal of Ni2+and Cd2+from water. Its adsorption behavior and mechanism was investigated. The effects of temperature, pH, calcium ion, magnesium ion and natural organic matters on adsorption were also investigated. A small mixed-flow-type adsorption reactor was designed to treat heavy metal wastewater continuously. The research above could provide technical support for the practical disposal of heavy metal water pollution accidents and the treatment of heavy metal wastewater. The main research contents and conclusions were shown as follows:(1) A novel spongy adsorbent was synthesized with PVA by grafting copolymerization and chemical modification. This new fibrous adsorbent was characterized by SEM, BET, EA, FT-IR and CNMR. The results indicated that the spongy adsorbent with hydroxamic group was hydrophilic with mainly meso-pore structure.(2) The novel spongy adsorbent could fast remove Ni2+and Cd2+from water. The chelating interaction between the sponge’s hydroxamic group and heavy metal ions was the main adsorption force. Freundlich model could fit the adsorption isotherms well and pseudo second order equation could better describe the adsorption kinetic process. The positive values of the enthalpy change indicated that the adsorption of Ni2+and Cd2+was an endothermic process. The negative values of the free energy change of Ni2+and Cd2+removal with the novel spongy adsorbent indicated that the adsorption reaction was a spontaneous process and the positive values of the entropy change indicated that the adsorption reaction was propelled by the entropy. What’s more,0.1M hydrochloric acid or EDTA solution could desorb Ni2+and Cd2+from the sponge effectively.(3) The removal of heavy metal ions increased when temperature increased. The higher uptake capacity of Ni2+and Cd2+by the novel spongy adsorbent was achieved at higher pH values, and the lower uptake capacity of Ni2+and Cd2+was observed in an acidic medium. Although the presence of alkali-earth metal ions in solution decreased Ni2+and Cd2+removal, the sponge still retained most of its adsorption capacity. Natural organic matters had hardly negative effects on Ni2+and Cd2+removal with the sponge.(4) During the continuous adsorption process which was well described by the "ideal process" of the mixed-flow-type adsorption reactor, the presence of alkali-earth metal ions and natural organic matters in the certain concentration range had little effect on Ni2+and Cd2+removal.