Sorption of platinum elements by carbon composite from hydrochloric acid solution of the refining plant
Abstract
The article is dedicated to the study of the dynamic sorption characteristics of carbon composite in comparison with VSK activated carbon, acting as the basis of the composite, and granular carbonised microporous Lewatit АF-5 adsorbent.
Sorption concentration of platinum metals from the technological solution of the refining plant was performed in dynamic conditions. Before the sorption experiments, the carbon sorbents were contacted with deionised water for 3 hours, after which the sorbents were placed into a sorption column and conditioned with hydrochloric acid with a concentration of 2 M in a dynamic mode for 3 hours at a rate of 3 C.V./h. After conditioning, the initial solution was passed through the sorption column at a rate of 1 C.V./h for 30 minutes. The solution released from the column was selected using fraction collector so that the volume of one fraction was 2 C.V. (column volume). Concentrations of platinum elements in solutions were determined by inductively coupled plasma atomic emission spectrometry.
Total dynamic capacities of the carbon composite, the initial activated carbon, and the Lewatit AF-5 sorbent were 1.59 mg/g (0.546 mg/cm3), 1.59 mg/g (0.535 mg/cm3), and 0.77 mg/g (0.462 mg/cm3) for platinum, and 26.7 mg/g (9.16 mg/cm3), 25.8 mg/g (8.68 mg/cm3), and 15.4 mg/g (9.24 mg/cm3) for palladium, respectively.
The degree of platinum sorption by the initial VSK activated carbon, carbon composite, and Lewatit AF-5 adsorbent was determined and amounted to 35.7, 37.7, and 32.2%, respectively. The degree of palladium sorption by these materials was 38.4, 39.4, and 40.9%, respectively.
To determine the dynamic characteristics of platinum and palladium sorption, we used the Thomas, Yoon-Nelson, and BDST (bed depth service time) models. The highest value of the determination coefficient (0.9736) was observed when processing the data of the output curve of palladium sorption by the carbon composite according to the Thomas model. Thomas constant KТ was 5.57∙10-4 dm3/(mg·h).
A 5% thiourea solution in 0.5 M HCl and aqua regia were used to elute platinum elements from carbon materials. Desorption of platinum elements with thiourea was conducted in dynamic conditions, and the desorbing solution was passed bottom up at a rate of 1 C.V./h for 10 hours at a temperature of 55°C. The concentration of elements in thiourea eluates did not exceed 0.04 mmol/dm3 for platinum and 0.27 mmol/dm3 for palladium.
Desorption of platinum elements with aqua regia solution was performed in static conditions with constant stirring, a temperature of 100°C, and a sorbent to eluent phase ratio of 1 : 4.5. The concentration in the eluate ranged from 0.50 to 0.75 mmol/dm3 for platinum and from 19.8 to 22.1 mmol/dm3 for palladium.
The average value of the concentration ratios of platinum and palladium during their desorption with aqua regia from a carbon composite and VSK activated carbon was 3.0, which stood in contrast with the values for the AF-5 adsorbent the desorption of which resulted in the concentration ratio of 2.0 for platinum and 2.9 for palladium.
Thus, it can be concluded that it is possible to extract platinum metals by the selected carbon composite from complex solutions of the refining plant with their further elution with an aqua regia solution.
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References
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