Thermal Decomposition of Ktenasite Термична Декомпозиция На Ктенасит

СПИСАНИЕ НА БЪЛГАРСКОТО ГЕОЛОГИЧЕСКО ДРУЖЕСТВО, год. 81, кн. 3, 2020, с. 25–27 REVIEW OF THE BULGARIAN GEOLOGICAL SOCIETY, vol. 81, part 3, 2020, p. 25–27 Национална конференция с международно участие „ГЕОНАУКИ 2020“ National Conference with international participation “GEOSCIENCES 2020” https://doi.org/10.52215/rev.bgs.2020.81.3.25 Thermal decomposition of ktenasite Термична декомпозиция на ктенасит Zlatka Delcheva1, Nadia Petrova1, Tsveta Stanimirova2 Златка Делчева1, Надя Петрова1, Цвета Станимирова2 1 Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, 107 Acad. G. Bonchev Str., 1113 Sofia, Bulgaria; E-mail: [email protected] 2 University of Sofia “St. Kliment Ohridski”, Faculty of Geology and Geography, Department of Mineralogy, Petrology and Economic Geology, 15 Tzar Osvoboditel Blvd., 1000 Sofia, Bulgaria Keywords: ktenasite, thermal decomposition, decomposition products. Introduction mal behavior of Cu-hydroxy-salt minerals has been poorly studied. The ktenasite is a copper zinc hydroxy-sulfate- The aim of this paper is to report preliminary hydrate mineral first found by Kokkoros (1950) in data concerning the thermal behavior of the ktena- the Kamariza mine, Lavrion (Greece). This min- site based on analysis of decomposition processes eral occurs as an alteration products of copper-zinc and obtained products using combined thermal and ores and slags. The crystal structure of ktenasite XRD methods. was solved by Mellini and Merlino (1978) in space group P21/c and characterized by interrupted sheets 2 – Experimental ∞[(Cu, Zn)2(OH)3O] of distorted copper-zinc octahedra. Sulfate groups are connected to both sides of The ktenasite was prepared by a chemical reaction the octahedral sheet by corner sharing. The resultant between 1 g of ZnO powder and 10 ml 1M solu- composite tetrahedral-octahedral sheets own nega- tion of CuSO4 with periodical steering at room tem- tive charge, which is compensating by interlayer perature for 7 days. The obtained suspension was 2+ [Zn(H2O)6] octahedra through a system of hydro- filtered, washed with distilled water, and dried at gen bonds. There is a known series of minerals with room temperature. ktenasite type structure: serpierite, devilline, nieder- The DSC-TG analyses were carried out on appa- mayrite, edwardsite, kobyashevite, campigliaite and ratus SETSYS2400, Evolution, SETARAM at the others. For the first time ktenasite was synthesized following conditions: temperature range from 20 to by Xue et al. (2004) using simple method of mixing 1000 °C, in a static air atmosphere, with a heating –1 ZnO powder with CuSO4 solution at room tempera- rate of 10 °C min , and 10–15 mg sample mass. Si- ture and characterized by different analytical meth- multaneous analysis of the evolved gases was per- ods in order to evaluate its intercalation processes. formed via mass spectrometry using an OmniStar Some data on the thermal behavior of the ktenasite mass spectrometer connected to the TG apparatus. can be find in that paper. The phase composition of the initial sample and There is no detailed analysis in the literature products obtained during thermal decomposition toward the processes, the solid products and vola- was studied by powder X-ray diffractometer D2 tiles during the ktenasite thermal decomposition. Phaser Brucker AXS with Cu-Kα radiation in steps It is known that the thermal decomposition of cop- of 0.02° s–1. per hydroxide sulfates and zinc hydroxide sulfates leads to the formation of CuO (Koga et al., 2008) Results and discussion and ZnO (Moezzi et al., 2013; Liang et al., 2015), respectively as final products with various desired Data of the DSC-TG (DTG)-MS and the XRD pat- properties and applications. In contrast to the de- terns of the initial ktenasite and the products of its tailed characteristics of the thermal decomposition thermal decomposition are shown on Fig. 1A–B. of various Zn-hydroxy-salt minerals with the final The XRD data of the synthesized ktenasite (Fig. 1 B) product ZnO (Stanimirova et al., 2016), the ther- bottom) correspond to the reference in the ICSD 25 database (PDF No 83-2247). The reflections of the ecules play role of charge balancing bridge between 2+ 2– synthesized ktenasite are comparable to those of Zn and O atoms from SO4 . Apparently, the in- synthetic ktenasite reported in the literature (Xue et teraction of the water molecules with the Zn cation al., 2004; Stanimirova et al., 2019). On the XRD and the oxygen atom of the sulfate group causes pattern of the initial sample, a small amount (about a different energy of stage-by-stage dehydration. 5 mass% estimated by program PowderCell) of bro- Two H2O molecules leave the ktenasite structure chantite (PDF No 84-0454) is also registered. Prob- according to the data from the TG analysis within ably, its appearance is due to intensive washing of the endo-effect 1. At that time, the XRD data show the ktenasite precipitate following synthesis. For an interlayer shrinking of 1.33 Å (d002 from 11.78 to such transformation of ktenasite into brochantite 10.45 Å), Fig. 1B), which is evidence for the pres- through leaching of the ion pair (the interlayer M2+ ence of partially dehydrated form of ktenasite. The 2– and the hydroxide layer bonded SO4 ) under water analysis of the XRD data shows that this partially treatment was recently reported (Stanimirova et al., dehydrated phase is isostructural with the mineral 2019). christelite, also a layered Cu-Zn hydroxy sulfate Dehydration: In the low-temperature interval composed by a ktenasite-type hydroxide layer. In (20–380 °C), four endo-effects on the DSC-curve christelite structure the interlayer Zn cation is also are registered (Fig. 1 A, 1–4), which suggests a octahedral coordinated, but octahedron consists of complicated process of dehydration. The MS analy- 4H2O and two oxygen atoms from two adjacent sul- sis shows leaving only of water molecules in this re- fate groups. gion. The water molecules of the ktenasite structure The next dehydration of the ktenasite (in the are not in free stage in the interlayer and octahedral framework of endo-effects 2 and 3) leads to the coordinate the Zn cations. Some of the water mol- formation of antlerite (PDF No 76-1621), an anhyd- Fig. 1. DSC-TG-MS data: A, for Ktenasite and powder XRD patterns; B, of initial and thermally treated samples. Initial and product samples of thermal decomposition were marked as follows: Kten – ktenasite; Cri* – isostructural with christelite partial dehydrated ktenasite; Ant – antlerite; Gun – gunningite. The impurity brochantite is marked with ● 26 rous copper hydroxy sulfate mineral and gunningite SO4 degradation: This process proceeds in the (PDF No 74-1331), a zinc sulfate monohydrate min- temperature interval 700–1000 °C in the range of eral, Fig. 1B). Apparently, the departure of three endo-effects 7 and 8 on the DSC curve. MS analy- more water molecules from the environment of the sis data show the presence of SO2 and O2 as evolv- interlayer Zn cation enhances the interaction of Zn2+ ing gases. The effect 7 points the decomposition of cations with the sulfate groups, separating them Cu2O(SO4) (Koga et al., 2008) followed by the de- from the hydroxide layer and forming gunningite. composition of Zn3O(SO4)2 (endo-effect 8) (Strasz- After this process, half of the sulfate anions remain ko et al., 1997; Stanimirova et al., 2016). Tenorite in the hydroxide layer, as the quantitative ratios of (CuO) and zincite (ZnO) are obtained as final prod- 2+ 2- Zn and SO4 in the ktenasite structure are 1:2. The ucts of the thermal decomposition. calculated losses in the range of 2 and 3 endo-ef- Finally, we may conclude that the thermal de- fects have a yield of about 3.5 H2O (Fig. 1A). The composition process of the ktenasite including dif- higher amount of the water released is a result of ferent processes such as dehydration, dehydroxyla- the restructuring of the hydrate-free hydroxide layer tion and evolving of SO2 and O2 is rather compli- (type brochantite Cu4(OH)6SO4) into an antlerite cated due to the simultaneous presence of both cop- layer (Cu3(OH)4SO4), which is associated with the per and zinc in the system and this suggests further separation of one OH group. The gunningite losses investigations to clarify the reaction mechanism of its water molecule within endo effect 4 in the same the process. manner and the temperature range of 250–350 °C us in the publications of Straszko et al., (1997) and Po- Acknowledgements: This work was supported sern et al. (2014). As can see from DSC-TG curves by the Bulgarian Ministry of Education and Science both dehydration and partial dehydroxilation finish under the National program “Young scientists and up to 380 °C. We take in consideration as well the postdoctoral students”. presence of brochantite (5 mass % in the initial sample) and in this way 6.4 H2O molecules leave the References system up to 380 °C. Thus, the scheme of thermal decomposition in the low temperature region (1–4 Koga, N., K., A. Mako, T. Kimizu, Y.Tanaka. 2008. Thermal decomposition of synthetic antlerite prepared by micro- endo-effect) can be described as follows: wave-assisted hydrothermal method. – Thermochimica 20 100 C Acta, 467, 11–19. ZnCu4(OH)6(SO4)2·6H2O 2H O଴ Kokkoros, P. 1950. Ktenasit, ein Zink-Kuprefersalt aus Lavrion ൊ (Griechenland). – Tschemarks Mineral. Petrogr. Mitt., 3, ଶ 1, 342–346. ZnCu4(OH)6(SO4)2·4H2O െ � �� C Liang, W., W. Li, H. Chen, H. Liu, L. Zhu. 2015. Explor- � 250 350 C ing electrodeposited flower-like Zn (OH) SO .4H O na- ZnSO ·H O + 1.25Cu (OH)��SO �� 4 6 4 2 4 2 3 4 4 H O ଴ nosheets as a precursor for porous ZnO nanosheets.

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