Optimized procedure to obtain high-purity calcium salts from hen’s eggshells for the food industry. The invention enables to produce tricalcium phosphate, calcium citrate tetrahydrate, calcium lactate pentahydrate, calcium malate and calcium citrate malate, food additives that can be used for the calcium intake. Purity levels achieved can exceed the 70% of the obtained product. Further, eggshell waste no longer needs to be throw away or taken to landfills, reducing the pollution.