电镀污泥钠钙化焙烧过程金属的矿相转化及平衡分布

Metal phase transformation and equilibrium distribution in sodium roasting process of the electroplating sludge

电镀污泥钠化焙烧过程,由于Al、Cr和Zn的氧化物易与Fe_2O_3反应生成铁酸盐及其他复杂含铁盐类,导致灰渣水浸过程其浸出率较低。在添加剂CaO作用下,采用FactSage软件模拟污泥焙烧过程金属的矿相转化规律,找到提高Cr、Al和Zn浸出率的方法。研究结果表明,污泥钠化焙烧过程,添加剂CaO易与Fe_2O_3反应生成2CaO·Fe_2O_3,阻止Fe_2O_3与Cr、Al和Zn的氧化物反应生成铁酸盐及其他复杂盐类,一定程度上提高了Cr、Al和Zn的浸出率。但高温下,Al_2O_3也易与Cr、Al和Zn的氧化物反应生成难溶性铝酸盐,所以浸出率提高幅度不大。可采用稀碱先脱除污泥中的铝,铝的浸出率达95%以上,脱铝渣再拌苏打和CaO焙烧,灰渣水浸脱铬率达95%以上。通过分析可知,污泥在焙烧之前脱铝和在焙烧过程铁转化成2CaO·Fe_2O_3,阻止了难溶性铝酸盐、铁酸盐以及其他复杂盐类的生成,同时Cr和Al得到分离,且灰渣中铜、镍和锌以游离氧化物和极少部分结合氧化物形式存在,有利于后续金属的浸出和分离。

In the process of sodium roasting of electroplating sludge, oxides of Al, Cr and Zn can easily react with Fe2O3, which leads to the formation of ferrate and other complex iron salts, and then reduces their leaching rates in ash slag with water. The FactSage software was used to simulate the mineral phase conversion discipline during the sodium roasting process under the additive CaO, and the methods for leaching rate increasing could be obtained. The results show that CaO can easily react with Fe2O3 to form 2CaO·Fe2O3, to a certain extent, which can prevent the formation of ferrate and other complex salts from the reaction between Fe2O3 and Cr, Al and Zn oxides to a certain extent, and their leaching rates increased. However, at high temperature, Al2O3 can also react with oxides of Cr, Al and Zn to produce the insoluble aluminates, thus, their leaching rates are slightly increased. When the dilute alkali was used to leach Al from sludge, its leaching rate reached above 95%. Afterwards, the de-aluminate slag was roasted with soda and CaO, the leaching rate of Cr by water could reach over 95%. Based on the above analysis, removal of Al before the sludge roasting and iron conversion to 2CaO·Fe2O3 during the roasting process that can prevent the formation of the insoluble aluminates, ferrates and other complex salts. At the same time, Cr and Al are separated, and free oxides and a small quantity of binding oxides of copper, nickel and zinc metals remained in the ash slag, which was beneficial for the subsequent metal leaching and separation.