Modern Trends in the Technology for Producing Granular Calcium Nitrate with Reduced Hygroscopicity from Local Limestone Raw Materials: A Critical Narrative Review

Abstract

Calcium nitrate is an agronomically valuable, rapidly soluble source of nitrate nitrogen and calcium, yet its pronounced hygroscopicity, deliquescence and tendency to cake create persistent manufacturing, storage and distribution problems. These limitations are particularly important when calcium nitrate is produced from locally available limestone because mineralogical variability, magnesium and silicate impurities, acid consumption, solution purification and water management all influence the crystallisation and granulation behaviour of the final product. This critical narrative review evaluates modern technological strategies for producing granular calcium nitrate with reduced hygroscopicity, with emphasis on limestone–nitric acid routes relevant to regions seeking to localise fertiliser manufacture. Literature was searched across Google Scholar, Semantic Scholar, DOAJ, Crossref, OpenAlex and AGRIS, supplemented by forward and backward citation searching, for publications available up to 26 June 2026. The evidence indicates that no single intervention eliminates the moisture sensitivity of calcium nitrate. Instead, successful process design depends on an integrated sequence: rigorous limestone characterisation, controlled nitric-acid decomposition, management of free acidity and insoluble residues, concentration without excessive hydration, granulation under a narrow liquid-phase window, careful drying and cooling, and post-granulation surface conditioning. Hydrophobic wax-, oil- and amine-containing coatings can markedly reduce moisture ingress and caking in nitrate fertilisers, while mineral modifiers may improve granule structure and alter water activity; however, evidence specific to pure or near-pure calcium nitrate remains considerably thinner than evidence for ammonium nitrate and calcium ammonium nitrate. Local limestone can provide a technically credible feedstock when carbonate purity and impurity profiles are controlled, but claims of universal transferability are not justified. The most defensible modern approach is therefore feedstock-specific process integration supported by humidity-response testing, crushing-strength measurement, phase analysis and storage simulation rather than reliance on composition alone. Future work should prioritise pilot-scale validation, environmentally acceptable coatings and quantitative links between mineral impurities, hydrate phase behaviour and long-term granule stability.