FLOTATION OF CHRYSOCOLLA a thesis submitted for the degree of PhD in Engineering in the University of London by Anthony John. Wright BSc(Eng) -partment of Mining and Mineral Technology Royal School of Mines London SW7 Janaary 1964 2. 1. SUMMARY. The existing information on the mineralogy and beneficiation of the hydrated copper silicate mineral, chrysocolla, has been critically analysed in conjunction with new data here determined on a typical specimen of the mineral obtained from the Kolwezi mine of Union Miniere du Haut Katanga. It is concluded that chrysocolla is a rigid xerogel with a crystallite size of 150 R. The most important physical property of the Kolwezi chrysocolla is its ability to sorb and desorb water: this supposes a porous structure, which has been confirmed.. The pores, which have an average diameter of 35-40 .g account for 40% (by volume) of the mineral. The relationship between the structure and solubility of chrysocolla, and its behaviour in xanthate and sodium sulphide - potassium xanthate flotation systems has been thoroughly investigated. It is concluded that flotation of chrysocolla is possible in either system, providing that large quantities of reagent are used and that the flotation conditions are quiescent. More turbulent flotation conditions reduce the floatability of chrysocolla by scouring the ' hydrophobic species from the external surface. In both quiescent and turbulent flotation conditions, the major portion of the hydrophobic species is formed either in the bulk solution or within the mineral pores, and not at the external mineral surface. The hydrophobic species are coprecipitated cuprous xanthate and dixanthogen. The effect of soluble sulphide is to reduce the subsequent reaction between potassium 3• xanthate and chrysocolla: no appreciable reaction occurs between precipitatedcupric sulphide and potassium xanthate. Improved plant practice is considered possible providing the attrition of chrysocolla is minimised and reagent concentrations are maintained at high levels. 4. 2. INTRODUCTION. Hydrous copper silicate minerals of the chrysocolla group are not industrially selectively recovered by flotation, despite the fact that various workers (e.g. 1 4 \ Arbiter , Bowdish and Chen`, Jaekel3 and Kovacs ) have shown flotation to be possible in laboratory-scale investigations. It is particularly noted that many of the successful laboratory investigations are similar in some - even many - respects to the familiar sulphidation- xanthate process by which copper (and lead) carbonate minerals have been successfully beneficiated for a number of years on an industrial scale. Chrysocolla, however, is not apparently amenable to the industrial sulphidation- xanthate process. The mechanism of successful laboratory processes and the reasons behind their industrial inapplicability, have been largely ignored by many workers in this field. Typically (e.g. Dean-5-, Jal,kel3 and Ludt and Dewitt6), they have confined their researches to an assessment of floatability after some specific conditioning process. In the work described here, a more fundamental approach has been attempted. The aim of this research has been to define the basic physical, physico-chemical and chemical properties of a particular sample of chrysocolla, and show how these may preclude the satisfactory recovery of chrysocolla in present-day industrial flotation systems. Thus, it has not been the intention here to define the conditions for the successful industrial flotation of the Kolwezi chrysocolla. However, the work has suggested certain improvements which might be advantageously applied to the treatment of ores in which chrysocolla is a constituent. 5. 3. NOMENCLATURE. In 1950, Hey7 considered that the data available on hydrous copper silicates pointed to the existence of only three distinct varieties, that is dioptase, plancheite and chrysocolla. More recent work by Neumann et alb and Poljak and Gordillo', however, has revived the earlier contention that a further variety, shattuckite, is distinguishable. In order that the properties of chrysocolla may be more readily distinguished, the essential properties of these other hydrous copper silicates are now briefly discussed, and summarised in Table 1. The physical and optical properties ofaoptase have 10 been well-described by Dana . It is a transparent, emerald-green mineral having hexagonal symmetry. X-ray powder diffraction data are reported by the ASTM powder 11 12 data file , Billiet and Neumann et a18, although the data of Neumann et alb are not in accord with those of the other two sources. The crystal structure of dioptase has been deduced by Belov et a113, Heidel4 and Moenke15, who conclude that the basic structural unit consists of six silicon-oxygen tetrahedra in a ring formation. Differential thermal analyses showing good agreement 16 have been reported by both Ivanova and Toussaint The principal feature of these analyses is an endothermal effect at approximately 550°C caused by the loss of structural water. The mineral is generally represented by the formula Cu6(Si6018). 6H20. Although plancheite is not so well established as a distinct species, it is generally described as a pale- blue mineral having orthorhombic symmetry. Concordant x-ray powder data for various samples of the mineral are 6. TABLE 1: PRINCIPAL PROPERTIES OF DIOPTASE AND PLANCHEITE. MINERAL DIOPTASE PLANCHEITE Colour Emerald-Green Pale-Blue S.G. 3.3 - 3.4 3.3 - 3.8 Crystal System Hexagonal Orthorhombic R.I. 1.64 - 1.71 1.64 - 1.72 2.11 3.32 d spacings - 2.60 3.50 7.24 4.40 DTA peaks °C 550 endo. 300 exo, 670 endo 7. 12 19 reported by Billiet , Guillemin and Pierrot18, Millman , 20 and cumin and Lasheva . The principal 'd' spacings are at 3.32, 3.50 and 4.40 R, although the work of Neumann et alb doesnot agree with these values (c.f. dioptase). Only Toussainti7 has recorded a differential thermal analysis for a plancheite sample: it shows a broad exothermal peak at 300°C, and a sharp endothermal peak at 670°C. Evidence that shattuckite is a distinct species is 21 put forward by Ford , Neumann et alb and Poljak and 21 Gordillo9. Ford describes shattuckite as being more dense than plancheite (e.g. 3.8 against 3.3), and having higher refractive indices (c.1.78 against c.1.66). Neumann et al8 and Poljak and Gordillo9 quote x-ray powder data which are different from those of dioptase, plancheite (and chrysocolla), although the two sources 12 22 are not in agreement. Although Dilliet , Sun and Toussaint17 claim the identity of shattuckite as a distinct species, their published data agree very well with that of plancheite.. Clearly, plancheite and shattuckite are closely related, if not identical, on the evidence presented here. The composition of these minerals, which for convenience will be termed plancheite, varies from 5Si02.6Cu0.1.5H20 to 14CuSiO3.6H2O. Hydrous copper silicates which do not conform to the above-mentioned properties (see Table 1) of dioptase and plancheite may be described under the group heading of chrysocolla. Different samples of this group, whilst manifesting various external forms and having different chemical compositions have been shown to exhibit very similar fundamental properties. Semmons23, in 1878, was 8. the first to suggest a chrysocolla group of minerals; but at that time - and for many years to follow - inadequate mineralogical techniques precluded the determination of any but the most superficial of properties, and his suggestion was somewhat impractical. Present-day methods of evaluating basic properties by x-ray and electron diffraction, differential thermal analysis, infra-red spectroscopy and thermogravimetric analysis enable the Semmons23 classification to be implemented. Included in the chrysocolla group of minerals are the previous designations asperolite 10‘ (Dana ),cornuite (Rogers2424, ), katangite (Billiet) and 10 pilarite (Dana ). 9. 4. REVIEW OF CERYSOCOLLA MINERALOGY a. Formation and occurrence. Hydrous copper silicate minerals, including chrysocolla, are of epigenetic origin, and similar materials have been synthesised by Belov et a125 and Shcherbina and Ignatova26. Their methods involved the dehydration of gelatinous precipitates produced by reacting a solution of a copper salt with a solution of sodium metasilicate under alkaline conditions. Chrysocolla is frequently found either in massive forms, or as pseudomorphs encrusting, or interlayered with other copper minerals. Chrysocolla occurs in many oxidised Copper orebodies, including those in Chile, Congo, South-west USA and the Urals in the USSR. The layered appearance of marry samples of chrysocolla 27 known as colloform banding, is considered by Edwards , to have resulted from either of two processes. Continuous precipitation may have occurred from solutions which periodically changedin copper or silica concentration, or precipitation may have resulted from solution evaporation, followed later by a fresh influx of solution. b. Constitution. Although Danal°, Winchell and Winche1128, Read29 and others represent chrysocolla by the formula CuSiO3.2H20, there are very few analyses in support of this. The majority of analyses show either an excess or a deficit of CuO, SiO 2 or H2O over the CuS103.2H20 formula, together with the frequent presence of other oxides especially A1203, Fe203, CaO or MgO. 31 23 After Foote and Bradley", Palmer and Semmons had noted the dependence of the.water content of 10. chrysocolla upon relative humidity, some mineralogists modified the formula CuSiO O. 3.2H20 to CuSiO3'nH2 However,