Development of Wet Recycling Process to Remove Tramp Elements from Scraped Steels

开发废钢中去除杂质元素的湿法回收工艺

基本信息

批准号：
11555181
负责人：
TSURU Tooru
金额：
$ 8.51万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

Many recycling processes for scraped steels have been proposed in these decades, however, wet processes to remove tramp elements are very rare because of their processing speed. We proposed again to use wet process based on electrochemical method to remove zinc and copper which are major harmful elements for using recycled steels. In a concentrated nitric acid solution, zinc and copper easily dissolved contrasting steel dissolution which are negligible by complete passivation of steels. Moreover, stability the passive films on steels in nitric acid depends upon the concentration of nitrate ions. We finally proposed a method to remove and recover coppers from scraped steels by using aqueous ammonia solution and electrolysis. In aqueous ammonia solution, copper and zinc dissolved as ammonia complexes in neutral to alkaline solution, however, iron remains stable passive state. To accelerate dissolution rate of copper, the scraped steels containing sufficient amount of copper was anodically polarized and the dissolved copper was deposited to the counter electrode by the same current. Current efficiency of the anodic dissolution was almost 100 % and that of cathodic deposition reached to 70 %. The purity of the deposited copper exceeds 99.9 %. In this research, we designed a bi-potentiostate having a capability of 50 A and 50 V of output. Using this, the electrode potential of the counter electrode also controlled to maintain a suitable deposition potentials for copper. To extend the acceleration of copper dissolution, anodic dissolution mechanism of copper was analyzed using a rotating disk electrode. The dissolution is controlled by diffusion of ammonia to the electrode in a stagnant condition. In a condition of eliminating diffusion effect, the rate determining step is found a chemical reaction following the electron transfer reaction.

近几十年来，人们提出了许多废钢回收工艺，然而，由于处理速度太快，去除杂质元素的湿法工艺非常罕见。我们再次提出采用基于电化学方法的湿法工艺去除再生钢中主要有害元素锌和铜。在浓硝酸溶液中，锌和铜很容易溶解，而钢的溶解度却可以通过钢的完全钝化而忽略不计。此外，钢上钝化膜在硝酸中的稳定性取决于硝酸根离子的浓度。我们最终提出了一种利用氨水溶液和电解从废钢中去除和回收铜的方法。在氨水溶液中，铜和锌以氨络合物的形式溶解，而在中性至碱性溶液中，铁则保持稳定的钝态。为了加快铜的溶解速度，将含有足够量铜的废钢进行阳极极化，并通过相同的电流将溶解的铜沉积到对电极上。阳极溶解的电流效率几乎为100%，阴极沉积的电流效率达到70%。沉积铜的纯度超过99.9%。在这项研究中，我们设计了一种具有 50 A 和 50 V 输出能力的双电位器。利用这一点，还可以控制对电极的电极电势以维持适合的铜沉积电势。为了延长铜溶解的加速速度，使用旋转盘电极分析了铜的阳极溶解机理。通过氨在静止状态下扩散到电极来控制溶解。在消除扩散效应的情况下，发现速率确定步骤是继电子转移反应之后的化学反应。