From The Study Of The Chromium Oxide Green, Chrome Tanning Waste Extract

Wasted chrome tanning liquors in tanneries are processed for the abstraction of chromium from it. How to use the chromium in it is one of the great problems faced the leather industry all over the world. There is plenty of chromium in it. The amount of chromium may be 3000-6000mg/l as the count of Cr2O3. The wasted chrome tanning liquors not only pollute the environment, but also does harm to human being's existence. In the meantime, a large amount of chromium resource is wasted.Several such useful techniques to process wasted chrome tanning liquors in tanneries as recycling, adsorbing, precipitating with flocculating agent, and precipitating with alkali are introduced. The first three means have many defects in the application, the last one has stopped only at the stage of getting Cr(OH)s.In the paper, experiments have been done to study the method of precipitating with alkali. If NaOH is used as precipitating reagents, pH value should be controlled at about 8,5, and precipitating temperature should be controlled at 40. At this time, Cr(OH)3 is a flocculent precipitation, the water processed reaches high quality, and the de-chroming rate of wasted chrome tanning liquors may be up to 99.9% in the proper condition. How to get Cr2O3 from Cr(OH)3 is studied and the best reaction condition is obtained at last. The conclusions show that the experiment may be affected by the reaction time and reaction temperature. If Cr(OH)3 is scorified at the temperature 1200 for seven hours , the purity of product may be 98.61%.By the way, the standard of chemical purity set by the National Chemical Industry Ministry is 98.5%; if Cr(OH)3 is scarified at the temperature of 1300癈 for seven hours, the purity of product can be 99.0%, and reach the standard of analytical purity(99.0%).By this method, both the problem of the pollution of wasted chrome tanning liquors and waste of resource are resolved. A new way of making CO is found in our country with rare chromium resources. The advantage of this method is perfect and the process is easy. Therefore, the method is easy for application. The perspective of it is wonderful, as is worthwhile of being believed.