Solubility product and heat of formation of lead alkyl xanthates by microcalorimetric titration A. Robledo-Cabrera, O.A. Orozco-Navarro, A. López-Valdivieso ⁎ Area de Ingeniería de Minerales, Instituto de Metalurgia, Universidad Autónoma de San Luis Potosí, Av. Sierra Leona 550, San Luis Potosí, S. L. P. 78210, México abstract article info Article history: Received 24 June 2014 Received in revised form 5 September 2015 Accepted 5 October 2015 Available online 9 October 2015 Keywords: Solubility product Heat of formation Lead xanthates Sulfide flotation Microcalorimetry Microcalorimetric titration of lead ions with various alkyl xanthate ions was used to determine the solubility product (K so ) and the heat of formation (ΔH 0 ) of lead alkyl xanthates (PbX 2 ). The titration was carried out at 25 °C in a 25 mL size isoperibol reactor containing lead aqueous solutions with an ionic strength of 0.01 M and pH 6. Sodium ethyl xanthate, potassium propyl xanthate, potassium butyl xanthate and potassium amyl xanthate were used in this study. A new relationship was found for the K so and the number of carbon atoms (N) in the xanthate alkyl chain, namely logK so = -10.033 - 1.049 N. The relationship between ΔH 0 and N was found to be ΔH 0 = -62.29 - 7.218 N, in kJ/mol PbX 2 . The K so and ΔH 0 values that were determined by microcalorimetry were compared to those theoretically calculated taking into account the transfer of the xanthate alkyl chain from the aqueous solution to the lead xanthate solid phase. There was an excellent agreement between theoretical and calorimetric ΔH 0 . Low deviation was found between theoretical and calculated K so . © 2015 Elsevier B.V. All rights reserved. 1. Introduction In the fundamental studies of the chemistry of sulfide flotation, knowledge of the solubility products (K so ) of metal-collector com- pounds is important because it is used to delineate the adsorption mechanisms of collectors onto the sulfide. Kakovsky (1957) report- ed the K so for various metal-collector compounds of interest in sul- fide flotation. He used potentiometric and solubility techniques to determine the K so of several metal alkyl xanthates and metal dialkyldithiophosphates. For lead alkyl xanthates, he reported a lin- ear relationship between logK so and the number of carbon atoms (N) in the chain length of the collector, namely logK so = - 14.2 - 1.21 N. The K so values given by Kakovsky (1957) have been amply accepted by the scientific community in flotation to explain the in- teraction between collectors and lead sul fide surfaces. Based on these K so values, conditions at which collectors chemisorb as mono- mers or precipitate as metal-collector have been established (Somasundaran and Wang, 2006; Fuerstenau et al., 2007). For lead ethyl xanthate, the K so given by Kakovsky is 1.7 × 10 -17 . Other K so values have been reported, however. Nanjo and Yamasaki (1969a,b) found a K so of 1.1 × 10 -15 , while Sheikh (1972) reported a value of 1.56 × 10 -16 . They used the solubility method to deter- mine K so . As noted, the K so values differ in one or two orders of mag- nitude from each other. Then, each K so value will lead to distinct calculated solubility of lead ethyl xanthate as well as to different lead ion-ethyl xanthate ion activity relationship for the formation of lead ethyl xanthate. Therefore, discrepancies will exist when ther- modynamic analyses are conducted on the adsorption mechanisms of ethyl xanthate on galena (PbS), cerussite (PbCO 3 ) and anglesite (PbSO 4 ). For lead xanthates with more than 2 carbon atoms in the xanthate alkyl chain only the K so values by Kakovsky (1957) have been reported. Microcalorimetry is a technique through which the heat of a chemical reaction, taking place in an aqueous solution, can be accu- rately determined (Christensen et al., 1972; Eatough et al., 1972a, 1972b; Hansen, 2003). It is based on the in-situ measurement of the temperature change in the aqueous solution due to heat released or withdrawn by the chemical reaction. This technique has been used in the mineral field to study the adsorption of ethyl xanthate on ga- lena (Mellgren, 1966; Partika et al., 1987; Persson and Persson, 1991), amyl xanthate on pyrite and marcasite (Haung and Miller, 1978), water adsorption on alumina (Griffiths and Fuerstenau, 1981) and recently of various sulfhydric-type collectors on galena (McFadzean et al., 2014). This work was aimed at the determination of the K so of various lead alkyl xanthates at 25 °C through titration isoperibol calorime- try. Through this technique, first both the heat of formation (ΔH 0 ) of the lead alkyl xanthates and the equilibrium constant (K 0 ) for the chemical reaction between lead and xanthate ions to form lead xanthate were determined. Then, the solubility product (K so ) of the lead alkyl xanthate was calculated from the K 0 value. The alkyl xanthates used in this work were sodium ethyl xanthate, potassium propyl xanthate, potassium butyl xanthate and potassium amyl xanthate. International Journal of Mineral Processing 144 (2015) 65–69 ⁎ Corresponding author. E-mail address: alopez@uaslp.mx (A. López-Valdivieso). http://dx.doi.org/10.1016/j.minpro.2015.10.003 0301-7516/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect International Journal of Mineral Processing journal homepage: www.elsevier.com/locate/ijminpro