Leaching of catalyst platinum from cured silicone elastomers: A preliminary study for comparing reagents

IF 4.8 2区 材料科学 Q1 METALLURGY & METALLURGICAL ENGINEERING
Tobias Feix, Aseel Ali Fadhil, Dennis Troegel
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引用次数: 0

Abstract

Addition curing systems involve two-part silicones which require the mixture of a silicone polymer with a catalyst to initiate the cure. Platinum is the most commonly used metal catalyst for addition curing of silicones by hydrosilylation which involves the crosslinking by the addition reaction of silicon hydride species to unsaturated bonds, mainly CC, but also CO or CN double bonds. After crosslinking of the polymers, the platinum catalyst cannot be recovered but remains in the silicone materials throughout the entire product life. In the end, platinum is disposed of together with the silicones and is thus lost to the value chain. The overall objective of this work was to develop a recycling process for the recovery of platinum from addition-cured silicone elastomers. In the first step, this was achieved by efficient digestion methods and by optimizing the leaching processes for exemplary commercial silicone elastomer products. Two different silicone materials were investigated, both of which were crosslinked with a platinum catalyst. The initial Pt content in the tested samples was 12.6 ± 0.2 mg/kg for a commercial silicone impression material and 6.3 ± 0.5 mg/kg for a silicone baking mold, measured by graphite furnace atomic absorption spectrometry (GF-AAS). Samples were first frozen with liquid nitrogen to improve brittleness and then crushed with a simple food processor to obtain a silicone granule. Various acid mixtures, mainly based on sulfuric acid, were investigated as digestion methods in order to extract platinum from the silicone network. These had different effects on the dissolution behavior of silicone samples and the amount of platinum extracted in each case. The amount of platinum leached from the filtrate of the digested samples in each case was measured by ICP-OES to evaluate the efficiency of different leaching mixtures. In addition, the dissolved platinum species present in the solutions was identified by UV/VIS as tetrachloridoplatinate(II) complex. The best platinum leaching results so far were obtained with two methods, both of which used a leaching mixture based on sulfuric acid and hexamethyldisiloxane (M2). In the presence of hydrochloric acid, 9.6 ± 1.6 mg platinum/kg was leached from the silicone impression material and 4.2 ± 0.8 mg platinum/kg from the silicone baking mold. With the additional use of aqua regia instead of hydrochloric acid, 10.4 ± 2.8 mg platinum/kg was extracted from the silicone impression material and 4.8 ± 1.0 mg platinum/kg was extracted from the silicone baking mold. These methods were replicated with n = 3. Using statistical evaluation methods (F-test, t-test, and confidence interval), no significant difference was found between these two best methods. Recovery of platinum(0) from leach mixtures has not yet been achieved due to high dilution and very low platinum concentration in samples and will be part of another study.

从固化硅树脂弹性体中浸出催化剂铂:比较试剂的初步研究
加成固化系统涉及双组分有机硅,需要将有机硅聚合物与催化剂混合以启动固化。铂是最常用的金属催化剂,用于通过氢化硅烷化作用对有机硅进行加成固化,即通过硅氢化物与不饱和键(主要是 CC 键,也包括 CO 或 CN 双键)的加成反应实现交联。聚合物交联后,铂催化剂无法回收,但在整个产品生命周期中都会留在有机硅材料中。最后,铂金与有机硅一起被废弃,从而在价值链中流失。这项工作的总体目标是开发一种从加成固化有机硅弹性体中回收铂的循环工艺。第一步,通过高效的消化方法和优化商用硅树脂弹性体产品的浸出工艺来实现这一目标。对两种不同的硅胶材料进行了研究,这两种材料都使用了铂催化剂进行交联。通过石墨炉原子吸收光谱法(GF-AAS)测量,商用硅胶印模材料和硅胶烤模样品中的初始铂含量分别为 12.6 ± 0.2 mg/kg 和 6.3 ± 0.5 mg/kg。样品首先用液氮冷冻以提高脆性,然后用简易食品加工机粉碎以获得硅胶颗粒。为了从硅胶网络中提取铂,研究了各种酸混合物(主要是硫酸)的消化方法。这些方法对硅胶样品的溶解行为和铂的提取量都有不同的影响。通过 ICP-OES 测量了每种情况下消化样品滤液中的铂萃取量,以评估不同萃取混合物的效率。此外,通过紫外/可见分光光度法(UV/VIS)鉴定了溶液中的铂溶解物为四氯铂酸(II)络合物。迄今为止,铂金浸出效果最好的方法有两种,这两种方法都使用了以硫酸和六甲基二硅氧烷(M2)为基础的浸出混合物。在盐酸存在的情况下,从硅胶印模材料中浸出的铂为 9.6 ± 1.6 毫克/千克,从硅胶烤模中浸出的铂为 4.2 ± 0.8 毫克/千克。用王水代替盐酸后,硅胶印模材料中铂的萃取率为 10.4 ± 2.8 毫克/千克,硅胶烤模中铂的萃取率为 4.8 ± 1.0 毫克/千克。这些方法以 n = 3 重复进行。使用统计评估方法(F 检验、t 检验和置信区间),发现这两种最佳方法之间没有显著差异。由于样品中的铂浓度很低,稀释程度很高,因此尚未从浸出混合物中回收铂(0),这将是另一项研究的一部分。
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来源期刊
Hydrometallurgy
Hydrometallurgy 工程技术-冶金工程
CiteScore
9.50
自引率
6.40%
发文量
144
审稿时长
3.4 months
期刊介绍: Hydrometallurgy aims to compile studies on novel processes, process design, chemistry, modelling, control, economics and interfaces between unit operations, and to provide a forum for discussions on case histories and operational difficulties. Topics covered include: leaching of metal values by chemical reagents or bacterial action at ambient or elevated pressures and temperatures; separation of solids from leach liquors; removal of impurities and recovery of metal values by precipitation, ion exchange, solvent extraction, gaseous reduction, cementation, electro-winning and electro-refining; pre-treatment of ores by roasting or chemical treatments such as halogenation or reduction; recycling of reagents and treatment of effluents.
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