| Based on the high chromium content of the high concentration chromium tanning wastewater,adding-alkali-magnetic-flocculation method was studied.Magnetic powder was used to speed up the setting rate of chromic hydroxide colloid,then the deposit was dissolved by acid and made into chrome powder,and the magnetic powder was separated.The chromium???hydrolysis ability was studied under different times,temperatures and dosages of alkali by evaluation of the chromium elimination ratio.The results showed that the favorable conditions of chromium???hydrolysis were the proportion of n?OH-?:n(Cr3+)was 4: 1,normal temperature,and hydrolyzing time was 30 min,and the chromium content of the treated chromium tanning wastewater was less than 30mg/L.The results showed that the settlement effect was the best under the proportion of m?magnetic powder?:m?Cr2O3?=1:1.The separation of magnetic powder was studied.The results showed that the separation of magnetic powder by filtration after the chromium hydroxide dissolved by sulfuric acid,which was complete.The chrome powder was prepared through drying.The properties of chrome powder was investigated through the measurement of moisture content,solubility,pH,Cr2O3 content,alkalinity,sodium sulfate content,sodium chloride content and organic compound content,process of making chrome powder was optimized,as well as its tanning effect was contrasted with that of industrial chromium powder.The results indicated that there were lots of differences between self-made chromium powder and industrial chromium powder,such as the contents of ingredients.Because of increasing dosage of self-made chromium powder,the shrinkage temperature of wet blue tanned by self-made chromium powder was similar with that of industrial chromium powder.But there were shortages of self-made chromium powder.Because of the low chromium content of the low concentration chromiumwastewater from neutralizing,retanning,dyeing,fatliquoring,etc.,the chromium???in simulated solution was removed by the bioflocculant,which was made from straw by microbial fermentation.The results indicated that the optimum conditions for chromium???elimination were temperature of 30?,p H of 7.5and reaction time of 40 min.Under the conditions,the chromium content of the simulated solution was less than 1.5mg/L.But the chromium removal performance of bioflocculant is affected by polyacrylate retanning agents,fatliquors and dyes in the wastewater,so the interfering substances in dyeing wastewater were removed by chrome tanning leather shavings,and the dechroming process by bioflocculant was optimized.The structure of bioflocculant and the principle of bioflocculant to remove chrome were analyzed.The results showed that:?1?The adsorption ability of bioflocculant was limited because of the low specific surface area;?2?Through the characterization of IR,UV and acid-base titration,the bioflocculant contained about 8 mmol/g carboxyl groups,which endowed it good solubility in alkaline solution and strong flocculation to cationic chromium complexes;?3?Under the alkaline condition,the carboxylic acid groups in the bioflocculant molecular chains had big degree of ionization and strong hydrophilic,and the chromium complex had strong hydrolysis and polymerization,so that the adsorption and bridging flocculation effect were produced,which was beneficial to chromium removal. |
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