Non-hydrothermal synthesis of copper-, zinc- and copper-zinc hydrosilicates

Abstract 

Cu/SiO₂, Zn/SiO₂ and Cu-Zn/SiO₂ samples have been prepared by the homogeneous deposition-precipitation method. The samples were analyzed by thermal analysis, X-ray diffraction and infrared spectroscopy after various heat treatments and compared with data obtained for several minerals. It has been shown that interaction between the components occurs through formation of hydrosilicates. Copper-silica system at a Cu:Si ratio ≤ 1, gives rise to a hydrosilicate stable up to a calcination temperature of 930 K resembling the mineral Chrisocolla; at higher ratios a hydroxonitrate (gerhardite type) is also formed. Zinc-silica interaction produces two hydrosilicates such as a well crystallized Hemimorphite at Zn:Si = 2 and highly dispersed Zincsilite at Zn:Si ≤ 0.75, both stable up to 1073 K. The Zincsilite structure consists of three layered sheets (an octahedral layer sandwiched by two tetrahedral ones) like the Stevensite mineral group. For the copper-zinc-silica system no copper hydrosilicate is formed. Copper merely enters the Zincsilite structure independenly of the applied (Cu + Zn):Si ratio. Resulting layered copper-zinc hydrosilicate may be described by formula

Zn_x-yCu_y(Zn_3-x–zCu_z–y▪_x)[Si₄O₁₀](OH)₂.nH₂O,

where Zn_3-x-zCu_z-y– ions are located in octahedral sites, Zn_x-yCu_y–ions in the interlayer; ▪_x are vacancies in the layers. Copper and zinc in excess of the Zincsilite ratio of Me:Si = 0.75, gives rise to copper and copper-zinc hydroxonitrates.