The possibilities of obtaining metallic calcium from Serbian carbonate mineral raw materials

Abstract

Article Highlights• Defined technological scheme of the calcium production from Serbian limestones • The influence of operating parameters on CaCO 3 calcination was examined • The dissociation is completed in 15 min at 1200 °C • The satisfactory rate for CaO aluminothermic reduction is accomplished at 1200 °C in 2 h • The content of hardly evaporated metals in obtained Ca is very low AbstractWe present experimental investigations that define both the technological scheme of calcium production from limestone by aluminothermic process and the basic operating parameters of the particular technological phases. The limestone with high content of Mg, Na and K was used in the study. X-ray analysis reveals that the samples contain mainly calcite with small amount of dolomite. At first, the effects of temperature, time and granulometry on the calcium carbonate calcination were examined. The dissociation process was completed in 10-15 min at 1200 °C, and the dissociation rate increased with decreasing particle size down to 5 mm. Afterwards, the aluminothermic reduction process of calcium oxide was investigated. At a temperature of 1200 °C and vacuum of at least 3 kPa, the reduction process completed within 2 h. The chemical composition of calcium oxide and calcium showed increased content of magnesium oxide and alkaline oxides (especially sodium).Pure calcium is a bright silvery-white metal, extremely soft and ductile. The metal oxidizes rapidly in the presence of moisture or in a dry air at temperature above 300 °C [1,2]. Calcium reacts readily with water, forming hydrated lime (calcium hydroxide) and hydrogen. It melts at 845 °C, boils at 1420 °C, and can be purified by distillation in an inert atmosphere or in a vacuum.Owing to its chemical reactivity with oxygen, calcium never occurs naturally in the free state although the compounds of the element are widely distributed among geological materials. The main calcium-bearing minerals are: the three carbonates -calcite, ara-

Analysis of Minerals as Electrode Materials for Ca-based Rechargeable Batteries

“…In addition to plagioclase feldspars (Na 1−0 Ca 0−1 Al 1−2 Si 3−2 O 8 ), the most abundant calcium minerals are carbonates (calcite and aragonite, CaCO 3 ; dolomite, CaMg(CO 3 ) 2 ), that constitute about 2.5% of the crust 11 , and sulfates (gypsum, CaSO 4 2H 2 O; anhydrite, CaSO 4 ). All these industrial minerals can be also used to obtain metallic calcium 12 which eventually forms the anode in the battery. The most common industrial procedure to obtain Ca metal is to treat the mineral with HCl to form CaCl 2 and a subsequent elecytrolisis process 13–15 .…”