钝化液中的锌对镀锌件铬酸盐钝化的影响及铬酸盐钝化液再生研究

发布时间：2018-11-18 06:27

【摘要】：铬酸盐钝化是当前批量热镀锌行业应用最广泛、性价比最高的处理方法之一,但是铬酸盐钝化液具有高致癌性,且其在使用一段时候后,钝化工件表面出现白色粉化物,影响了镀件外观,不得不定期更换钝化液,不但增加了企业生产成本,同时对环境产生很大的危害。由于目前无铬钝化技术在批量热镀锌行业的工业应用条件尚不成熟,因此寻求有效延长铬酸盐钝化液的使用寿命的方法,达到少排放甚至零排放,是热镀锌行业密切关注且亟待解决的问题。初步研究发现出现粉化现象与溶液中的锌离子浓度升高有关,因此本文以铬酸盐钝化液中的锌为研究对象,研究了锌对铬酸盐钝化产生的影响及影响机理、铬酸盐钝化液中的锌含量的测定方法、铬酸盐钝化液的再生。用SEM、EDS、XRD、XPS研究了锌对铬酸盐钝化膜形貌及成分的影响;用NSS、EIS、Tafel极化曲线测试研究了锌对铬酸盐钝化膜耐蚀性的影响。得出以下主要结论:1、研究发现,钝化液中锌离子的存在,使铬酸盐钝化膜上形成了较多的颗粒物,锌含量越高膜层表面颗粒物越多。膜层上颗粒物的锌氧比约为1:2。XRD分析发现,钝化液中锌的存在并不改变钝化膜的物质种类,钝化膜主要是以锌、铬化合物组成。XPS分析表明,随着溶液中锌离子含量增加,膜层O含量增加,Zn/Cr原子比上升,表明当铬酸盐钝化液中存在含量较高的Zn时,钝化膜中会形成较多的锌氧化合物。NSS、EIS、Tafel均表明,钝化液中锌的存在有助于提高铬酸盐钝化膜的耐蚀性。提出了锌对铬酸盐钝化产生影响的机理,认为铬酸盐钝化液中的锌会促进耐蚀性更好的膜层的形成。在空气成膜阶段,溶液中锌离子参与反应生成了颗粒物镶嵌在膜层中,形成致密度有别于内膜层的外膜层。2、开发了一种用EDTA滴定法测定锌含量的方法:用阴离子树脂交换除去钝化液中的Cr(VI),用铬黑T做指示剂,用EDTA二钠滴定锌含量。该滴定方法操作简单、测试成本低、重现性好、滴定终点易于判断,误差可控制在5%以内,可用于铬酸盐钝化液中含量在50~1400mg/L的锌的测定。3、通过静态吸附的方法,用732强酸性阳离子交换树脂再生铬酸盐钝化液,对交换时间、溶液p H值、树脂用量、溶液初始浓度、树脂再生性能进行了研究。该树脂能够选择性的吸附除去锌离子,但不会对钝化液中Cr(VI)含量产生影响。红外试验证实732强酸性阳离子交换树脂的吸附位置为磺酸基团(-SO3H),交换反应不引入其他杂质离子,且可下调钝化液p H值。732强酸性阳离子交换树脂的吸附速度快效率高,对Zn(II)的吸附符合单分子层吸附规律,具有饱和吸附性,饱和吸附量为85.6 mg/g。树脂的吸附性能和脱附再生性能良好,可实现树脂循环利用。该树脂再生铬酸盐钝化液的最佳p H为3~6。
[Abstract]:Chromate passivation is one of the most widely used and cost-effective treatment methods in batch galvanizing industry. However, chromate passivation solution has high carcinogenicity, and white powder appears on the surface of passivated workpiece after being used for a period of time. It not only increases the production cost, but also causes great harm to the environment because of the influence on the appearance of the plating parts and the need to replace the passivation solution regularly. Because the industrial application condition of chromium-free passivation technology in batch hot dip galvanizing industry is not mature at present, the method of effectively prolonging the service life of chromate passivation solution is sought, and the discharge is less or even zero. It is a hot-dip galvanizing industry to pay close attention to and urgent problems to be solved. It is found that the phenomenon of pulverization is related to the increase of zinc ion concentration in the solution. Therefore, the effect of zinc on chromate passivation and its mechanism are studied in this paper. Determination of zinc content in chromate passivation solution, regeneration of chromate passivation solution. The effect of zinc on the morphology and composition of chromate passivation film was studied by SEM,EDS,XRD,XPS and the corrosion resistance of chromate passivation film was studied by NSS,EIS,Tafel polarization curve. The main conclusions are as follows: 1. It is found that the existence of zinc ions in the passivation solution results in the formation of more particles on the chromate passivation film, and the higher the zinc content, the more particles on the surface of the film. The zinc-oxygen ratio of particles on the film was about 1:2.XRD analysis. It was found that the existence of zinc in the passivation solution did not change the species of the passivation film, and the passivation film was mainly composed of zinc and chromium compounds. XPS analysis showed that the passivation film was composed of zinc and chromium compounds. With the increase of zinc ion content in the solution, the O content of the film increases, and the Zn/Cr atom ratio increases, which indicates that more zinc and oxygen compounds will be formed in the passivation film when the content of Zn in chromate passivation solution is higher. The existence of zinc in passivation solution can improve the corrosion resistance of chromate passivation film. The mechanism of the effect of zinc on chromate passivation is put forward. It is considered that zinc in chromate passivation solution can promote the formation of better corrosion resistant film. At the stage of air film formation, zinc ions in solution take part in the reaction to form particles embedded in the film layer, forming an outer layer with density different from that of the inner membrane. A method for the determination of zinc by EDTA titration was developed. The content of zinc was titrated with EDTA disodium and chromium black T was used as indicator for the removal of Cr (VI), from passivating solution by anion resin exchange. The titration method is simple in operation, low in cost, good in reproducibility, easy to judge the end point of titration, and the error can be controlled within 5%. It can be used for the determination of zinc in chromate passivation solution in 50~1400mg/L. The chromate passivation solution was regenerated by 732 strong acid cation exchange resin. The exchange time, pH value of the solution, the amount of resin, the initial concentration of the solution and the regeneration performance of the resin were studied. The resin can selectively adsorb and remove zinc ion, but it has no effect on Cr (VI) content in passivation solution. The adsorption position of 732 strong acid cation exchange resin is sulfonic group (- SO3H), and no other impurity ions are introduced into the exchange reaction. The pH value of passivating solution can be down-regulated. The adsorption rate of 732 strong acid cation exchange resin is fast and high efficiency. The adsorption of Zn (II) conforms to the law of monolayer adsorption, and has saturated adsorption capacity of 85.6 mg/g.. The resin has good adsorption and desorption and regeneration properties and can be recycled. The optimum pH of chromate passivating solution regenerated by this resin is 3o 6.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4

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