Study On Preparation And Heavy Metals Ion Adsorption Properties Of Diatomite Adsorbent

The problem of heavy metal wastewater pollution is getting worse, and the mainsolutions include precipitation, electrolysis-electrodialysis and biological. Adsorptionis preferred for heavy metal wastewater treatment because of its easy operation, lowcost and no secondary pollution. Diatomite is an environmental friendly naturaladsorbent due to its high surface area, strong adsorption, well electronegativity insolution, and other special physics and chemical properties. However the adsorptioncapability of raw diatomite still needs to be improved and the studies on its processingand application on heavy metal ion are still expected to be carried out further.In this thesis, basing on the structure characteristics of diatomite，acid leachingpurification, mechanical force wet grinding and loading SiO₂were used to modifydiatomite structure, in order to improve its surface area and adsorption of heavy metalion. The study of preparetion technology, structure and properties of diatomiteadsorbent, the adsorption mechanism of heavy metal ion was carried out. The mainresults are as follows:（1） It was found that the surface area and pore diameter were increasing whentreated by acid leaching purification, mechanical force wet grinding and loadingSiO₂。After sulfuric acid leaching purification, the impurity was removed and SiO₂ofdiatomite increased from86%to96%, surface area up to17.47m²/g. Specific surfacearea of SiO₂/diatomite composite powder was27.25m²/g. The maximum grain size ofdiatomite decrease from130.37μm to7.24μm after mechanical force wet grinding,the range of particle size was between0.6μm and6μm, the surface area was16.08m²/g. Diatomite adsorbent prepared by different processing methods were used totreat lead, copper wastewater, and the results indicated that the diatomite produced bymechanical force wet grinding showed the best absorption efficacy. In the samecondition, removal rate of Pb（Ⅱ）、Cu（Ⅱ） increased from15.92%to96.88%,3.92%to60.40%, respectively.（2） The superfine diatomite as adsorbent to deal with heavy metals wastewaterand studied on the adsorption characteristic of Cu（Ⅱ）、Pb（Ⅱ）. The adsorption of heavy metals ion in diatomite strongly was influenced by the pH value of solution butlittle influence of the temperature. With the increasing of pH, amount of diatomiteand decreasing of the beginning concentration of heavy metals, the removal rate ofCu（Ⅱ）、Pb（Ⅱ） went up. The adsorption capacity of ultrafine diatomite increasedquickly in10minutes， and reach the adsorption equilibrium in20minutes of Pb（Ⅱ）and40minutes of Cu（Ⅱ）. Saturated adsorption of Pb（Ⅱ）、Cu（Ⅱ） are27.03mg/g，8.50mg/g, respectively. Langmuir modeling exhibited a better fit to the data forcopper and lead. The pseudo-second-order equation fitted well with the experimentaldata.（3） Based on the use efficiency and the economy, reused diatomite twice is quiteappropriate. Multilevel adsorption could save the dosage of diatomite and improveremoval rate. It wass very effective that the diatomite which adsorbed saturated wasdesorbed with the sour, as a result, the desorption rate had achieved above98%.Unfortunately, the adsorption capacity of desorbed diatomite was worse. Theadsorption mechanisms of heavy metal ions were proposed as adsorption byion-exchange action and surface complexation reaction.