Impact of Limestone Surface Impurities on Quicklime Product Quality

Abstract

Quicklime is produced through the thermal processing of limestone in industrial kilns. During quarry operations, fine particulate quarry dust adheres to limestone lump surfaces, increasing the bulk concentration of impurities in limestone products. During thermal processing in a kiln, impurities such as Si, Mg, Al, Fe, and Mn react with Ca, reducing quicklime product quality. Which reactant phases are formed, and the extent to which these result in a reduction in quality, has not been extensively investigated. The present study investigated as-received and manually washed limestone product samples from two operational quarries using elemental compositions and a developed predictive multi-component chemical equilibrium model to obtain global phase diagrams for 1000–1500 °C, corresponding to the high-temperature zone of a lime kiln, identifying phases expected to be formed in quicklime during thermal processing. The results suggest that impurities found on the surface of the lime kiln limestone feed reduce the main quality parameter of the quicklime products, i.e., calcium oxide, CaO (s), content by 0.8–1.5 wt.% for the investigated materials. The results also show that, in addition to the effect of impurities, the quantity of CaO (s) varies greatly with temperature. More impurities result in more variation and a greater need for accurate temperature control of the kiln, where keeping the temperature below approximately 1300 °C, that of Hatrurite formation, is necessary for a product with higher CaO (s).

Characterization of Limestone Surface Impurities and Resulting Quicklime Quality

“…The surface ma settled, and the excess water was decanted before drying at 105 °C. The procedure i described elsewhere [15]. The washed limestone pebbles (LSwashed) and the washing due (LSwashing residue) were weighed before further analysis.…”

“…This is reported to be more prominent in cold and wet conditions. In a previous study, it was presented that the surface impurities can reduce the quicklime quality (defined as the level of free lime, CaO(s)) up to 1.5 wt.-% according to multicomponent chemical equilibrium calculations [15]. In addition, for every 1 wt.-% of impurities in the limestone kiln feed, a reduction in free CaO(s) up to 4 wt.-% can be expected as a result of both diluting and reacting with the CaO(s) in the quicklime.…”

Analysis of the Ecological Footprint from the Extraction and Processing of Materials in the LCA Phase of Lithium-Ion Batteries

“…In the case of a lithium iron phosphate battery, the highest CO 2 emissions from the extraction and processing phase arise during the production of quicklime [73] (7759.28 m 2 a). A much smaller amount of CO 2 is emitted during heat production in an industrial furnace fuelled with hard coal [76] or during the cogeneration of heat and energy through natural gas in a conventional power plant (average 2541.31 m 2 a). The smaller emissions refer to the production of pig iron (762.96 m 2 a), sweet gas burnt in a gas turbine, heat production (natural gas in an industrial furnace), the operation of a hard coal mine [75], and the production of electricity through sintering (average 538.26 m 2 a).…”

“…Analysing NCM battery materials, the highest CO 2 emissions occur during the production of electricity with hard coal [76] (high-voltage electricity) (4111.20 m 2 a). Relatively slightly smaller emissions are generated during cogeneration of heat and electricity using natural gas (conventional) (3491.48 m 2 a).…”

“…Evaluation of the eco-efficiency of the use of battery technology in the production of electricity from coal [72] Carbon footprint reduction opportunities for electric vehicles and water vehicles [90] Possibilities of technology for storing electricity generated in coal-fired power plants [75] Proposals for optimizing electricity consumption during production, including achieving high production capacity and an electricity mix with low CO 2 emission intensity [76] Quicklime production (in pieces, loose)…”