Treatment of Sludge containing Chromium and Heavy Metals from Surface Finishing Recesses for Making it Harmless

表面处理工业废水处理后回收的污泥不仅含有大量的水，而且含有铬等重金属。为了减小该工业废弃物的体积和重量，并通过煅烧操作将污泥作为磁性材料回收利用，进行了本研究。目前已有研究指出，根据加热条件的不同，污泥中的铬在煅烧过程中可转化为有毒的六价态。在本研究中，首先发现六价铬的转化率在400℃左右有一个峰值，在400℃以下，煅烧污泥中的水分没有充分消除，晶体结构呈无定形，在400℃以上，污泥开始结晶，六价铬的含量减少。用纯氢氧化铬试剂在300℃下煅烧六价铬气的转化率大于k时，也得到了类似的结果。该污泥经900℃煅烧处理后，其六价铬含量较日本环境标准低。接下来，为了考察污泥中共存元素对六价铬转化率的影响，将镍、铜、锌、铁的氢氧化物试剂与氢氧化铬混合制成人工污泥，在200℃~ 700℃的大气中加热，并进行检测。结果表明，当其中一种氢氧化物与氢氧化铬混合并煅烧时，除氢氧化铜混合试验中六价铬含量有所降低外，共存元素对六价铬转化率没有明显影响。然而，当这些氢氧化物与氢氧化铬以与本研究中检测的实际污泥相似的摩尔比混合时，六价铬的转化率变得非常低，与实际污泥煅烧的结果相同。少

Sludge recovered from the waste water treatment of the surface finishing industries contains not only much amount of water but also heavy metals such as chromium. This study has been conducted in order to reducing the volume and weight of this industrial waste and to recycle the sludge as magnetic materials by the calcining operation. It has been pointed out so far that the chromium in the sludge can be converted to the toxic hexavalent state during the calcination according to the heating conditions.In this study, first of all, it became clear that the conversion ratio of hexavalent chromium has a peak at around 400℃ under which the water in the calcined sludge is not sufficiently eliminated and the crystal structure is amorphous like, and above which the sludge becomes crystallized and the amount of the hexavalent chromium decreases. The similar result has been obtained in the calcination of pure chromium hydroxide reagent where the conversion ratio of hexavalent chromium gas the pea … More k at 300℃. The content of hexavalent chromium became sufficiently low comparing with the environmental standard in Japan when the sludge examined was calcined at 900℃.In the next, in order to examine the effects of the co-existing elements in sludge on the conversion ratio of hexavalent chromium, artificial sludge was made by mixing hydroxide reagents of nickel, copper, zinc, and iron with chromium hydroxide, heated at 200℃ to 700℃ in atmosphere, and examined. It has turned out that when one of those hydroxides was mixed with chromium hydroxide and calcined, no significant effect of the co-existing elements on the conversion ratio of hexavalent chromium was found except for the copper hydroxide mixing test where hexavalent chromium content became lower to some extent. However, when the those hydroxides were mixed with chromium hydroxide in the similar molar ratio to the actual sludge examined in this study, the conversion ratio of hexavalent chromium became very low as same as the result of the actual sludge calcinations. Less