The possibility of using limestone instead of lime as an agent precipitating impurities from cobalt-rich solutions from the hydrometallurgical plants of Ruashi Mining in R.D. Congo was studied. These solutions come from the copper solvent extraction circuit and are intended for the production of cobalt hydrates. Precipitation tests performed in the laboratory have shown that limestone competes with lime in terms of precipitation of Fe, Mn and Cu impurities and co-precipitation of Co. The parameters which were exploited are: Eh, pH, time, % Solid and the particle size. Reduced to the equivalent quantities which enter into a precipitation reaction with 1.5 as the evaluated value of the limestone/lime ratio, the consumption of these two precipitating agents is almost the same. Co-precipitation of cobalt was acceptable and was limited to a yield of 3.0 % Co. Under these same conditions, copper was also removed with yields of around 40 %. The iron precipitated in good yields reaching over 90 %. On the other hand, Mn showed too low precipitation yields of less than 40 % by the fact that it required real oxidizing conditions which could bring it back to its insoluble form of MnO2. Finally, with the considerations on the cost of acquisition on the Ruashi Mining site of 160 and 50 USD respectively for the ton of lime and limestone, without integrating the cost linked to the fragmentation of the limestone to have the correct grain size, it is technically possible to substitute lime by limestone.