Kinetic studies of the removal of Pt(IV) chloride complex ions from acidic aqueous solutions using activated carbon

Reac Kinet Mech Cat (2017) 120:715–734 DOI 10.1007/s11144-017-1151-9 Kinetic studies of the removal of Pt(IV) chloride complex ions from acidic aqueous solutions using activated carbon Marek Wojnicki1 • Robert P. Socha2 • Magdalena Luty-Błocho1 • Krzysztof Fitzner1 Received: 8 November 2016 / Accepted: 1 February 2017 / Published online: 8 February 2017 Ó The Author(s) 2017. This article is published with open access at Springerlink.com Abstract In this paper, results showing the possibility of activated carbon application in platinum recovery from aqueous solution are presented. The studies were performed with the commercially available activated carbon, and the results can be easily transferred directly to the industry. The influence of pH, mixing rate, and amount of activated carbon as well as platinum(IV) initial concentration on the rate of adsorption was investigated. It was shown that after adsorption platinum is present on the surface of activated carbon in two oxidation states, ?2 and ?4, where shares of those forms are equal to 47 and 53%. Moreover, the enthalpy and entropy of activation were determined and are equal to 16.14 ± 075 kJ mol-1 and 42.19 ± 0.28 J mol-1 K-1. Keywords Adsorption  Platinum(IV) chloride ions  Recovery  Recycling Introduction Nowadays, the recycling of platinum group metals plays a very important role in the management of strategic resources. The number of primary sources of platinum is strictly limited. Therefore, the recycling of this metal is an important technological issue. Platinum is one of the most expensive metals among the platinum group metals (PGM). This is mainly due to its low production and its lack of substitutes in some areas. The main use of platinum is a widely understood to be in catalysis. Only & Marek Wojnicki 1 Faculty of Non-Ferrous Metals, AGH University of Science and Technology, 30 Mickiewicz Ave., 30-059 Krakow, Poland 2 Institute of Catalysis and Surface Chemistry Polish Academy of Sciences, Niezapominajek 8, 30-239 Krakow, Poland 123 716 Reac Kinet Mech Cat (2017) 120:715–734 in 2014, about 50.000 kg of platinum was recovered from automobile catalysts in the USA, while the world production of platinum is at the level of 160.000 kg per year. Also, a significant amount of platinum is used in jewels. However, the recycling in this area is not significant, mainly because of the long life of the products. The life time of the platinum based catalysts is estimated to be less than 1 year in the example of nitric acid production [1]. In this application, catalyst replacement is required every 3–12 months [2]. Platinum is also often used in hydrogenation and dehydrogenation reactions [3]. However, in those reactions, the catalyst can be poisoned by compounds such as S, P, As, Zn, Hg, halides, Pb, NH3, C2H2 [2]. The recovery of PGM can be achieved using several different methods [4, 5]. The pyrometallurgical method is mainly limited to PGM pre-concentration [6]. In the case of waste materials based on carbon, the pyrometallurgical method can be used for catalyst carrier removal. The most frequently applied method is based on a hydrometallurgical process consisting of several different stages. In general, there are three approaches to hydrometallurgical PGM recovery [7]. The first one is based on selective dissolution of the support materials. After this stage, the PGM-rich phase can be obtained, and next subjected to further hydrometallurgical processing. The second approach is based on the selective dissolution of catalysts without the dissolution of the support. This method is preferred. However, it can be applied only in a few cases. The third method is related to the total dissolution, i.e. carrier as well as catalyst. The platinum dissolution process is often carried out in cyanate [8, 9] or chloride [10–12] containing media as complex forming ligands. To remove platinum ions form aqueous solutions, several different methods can be used. One of the most promising method is based on ion exchange using different extractants, for example Cyanex 923 [13], Purolite S985, XUS 43600.00 and LewatitM ? MP 600 [10], Cyanex 471x [14]. An electrochemical method can be also used for PGM recovery [15–17]. However, this method has several significant disadvantages. Among them is the lack of selectivity, and in the case of chloride ion containing media, chlorine gas evolution. A reduction method can also be applied for precious metal recovery. For example, vitamin C [18, 19], sodium borohydrate [20], DMAB [21–23], hydrazine [24], ethanol [25], and methanol [26] can be used as reductants. First of all, those methods are not selective, i.e. it is impossible to separate PGMs using those methods. Moreover, it is also very difficult to separate PGMs from solutions containing base metals at elevated concentrations. Another very promising method for precious metal recovery is their adsorption on activated carbon (AC) and/or carbon based materials. Our previous studies were focused on the application of this method to gold [27, 28] and platinum [29] recovery using different types of activated carbons. Those studies were focused on the recovery of precious metals from acidic, chloride ion containing aqueous solutions. This topic was also investigated by others. Aktas and Morcali have shown that using AC, it is possible to remove 99% of Pt(IV) ions in time less than 1 h. [30]. It should also be noted that this method is efficient. It is possible to obtain a load of AC over 5% of PGM [31]. Chen et al. investigated the process of platinum ions adsorption on carbon fibers [32]. They have shown that the adsorption process is accompanied with the reduction of Pt(IV) to Pt(II) and next to Pt(0). It was 123 Reac Kinet Mech Cat (2017) 120:715–734 717 demonstrated that about 25% of Pt exists in the metallic state on the surface of AC fibers (ACF). On the one hand, this effect is advantageous because the efficiency of the process is higher, but on the other hand, strong oxidants have to be used to recover platinum. It seems that there is still too little work focused on platinum recovery from waste materials. This is mainly related to the fact that these studies are carried out by companies focused on precious metals recovery, which consider this knowledge as their confidential know-how. In this paper, we would like to investigate the possibility of AC application to platinum recovery from dilute acidic aqueous solutions. This method might be used to reduce metal losses in commonly applied technologies of precious metal refining and separation. Experimental In all our experiments, commercially available AC (AC) purchased from Norit(ROX 0.8) was applied in non-modified form. The platinum(IV) chloride complex was obtained according to the methodology described in the previous paper [29]. The measurements of the rate of Pt(IV) chloride complex ion adsorption onto AC were carried out in the cyclic glass reactor kept in the the (...truncated)