| In this paper, sewage sludge produced by waste water treatment was taken as raw material,based on the disadvantages of all kinds of traditional sewage sludge treatment,the phosphoric acid activation-microwave pyrolysis method was applied to obtain sludge adsorbent.The correlative problems during the preparation were worked out.And then,the adsorbent derived from sewage sludge was applied to the heavy metal chromium ions treatment process,and the application conditions were investigated in detail.Taking iodine adsorption value and Cr(Ⅵ)removal effect as the factors to reflect the performance of sludge adsorbent,sludge adsorbents were made in atmosphere of air and nitrogen respectively.Four different effect factors were studied and compared during the preparation process to inspect how they affect the performance of sludge adsorbents.The experimental results showed:the optimum preparation condition was that microwave power was 550W, irradiation time was 330s, phosphoric acid concentration was 40%,the phosphoric acid to raw sludge ratio was 2:1;the sludge adsorbent made in air(SAA) was better than the one made in nitrogen(SAN), but product ratio of the former was slightly lower than that of the latter. The sludge adsorbent(SAA) made under the best condition which showed the best performance was characterized by SEM/EDAX,FTIR and surface analyzer. It's found that the surface of SAA was rough,porous structure can be seen vividly;Main elements on the surface are C,O,Si and P;The FTIR study indicated that the adsorption peaks around 3420 cm-1 and 1638 cm-1 are assigned to-OH and C=O which are acidic oxygenous functional group;Compare to raw sludge,the surface area increased tremendously and porous structure was mainly mesoporous.All the changes of surface structure and chemical property can promote its application to wastewater treatment.Adsorption of Cr(Ⅵ)on sludge adsorbents were performed by batch experiments under different conditions.Significantly improving adsorptive removal efficiency of Cr(Ⅵ) were observed with the reduction of pH and the increase of adsorbent dosage. When the initial concentration of Cr(Ⅵ) rose from 10mg/L to 120mg/L,the removal efficiency of SAA and SAN were both high,the former decreased from 99.55% to 85.13% and the latter decreased from 99.28% to 78.28%.The adsorption procedure can be divided into two steps:the first one was the quick adsorption stage in which the removal efficiency increased with adsorption time linearly;the second one belonged to mid-latter stage in which the adsorption rate increased slowly until the equilibium.The kinetic data for Cr(Ⅵ) could be well described by pseudo-second order rate model.Both the initial adsorptive rate v0 and pseudo-second order rate constant k2 increased with the rising of temperature.Under three different test temperatures of 283K,293K and 303K,the data for Cr(Ⅵ)adsorption were well fitted to the Langmuir adsorption isotherm.Thermodynamic investigations showed that the adsorption of Cr(Ⅵ) on SAA was spontaneous and endothermic.The absolute value ofΔG0 increased with the rising of temperature,showing that this adsorption reaction is prone to happen at higher temperature.The activation energy was 9.214kJ/mol which could primarily prove that the adsorption of Cr(Ⅵ) to SAA was chemical adsorption.The mechanism of removal of Cr(Ⅵ) using sludge adsorbent can be explained by two effects.One is redox, Cr(Ⅵ)was reduced to Cr(Ⅲ)in acidic condition,and then be removed by ion exchange.The other one is surface complexation, Cr(Ⅵ) anion group mate with the hydroxyl group on the surface of sludge adsordent and be removed by adsorption.The experimental phenomena and characterization results can prove the rationality of this inferrer.
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