I do not know what could be other ingredients in the raw sample but if you take powdered raw sample containing calcium oxide and add dilute nitric acid and warm a bit the calcium oxide will dissolve, you can add portion wise the raw material till the acid gets neutralized. You can filter it and the filtrate on evaporation on a boiling water bath or low hot plate will finally yield solid calcium nitrate. This could be hygroscopic so you can dry this mass in a vacuum desiccator . You have not mentioned if the raw mass has other acid soluble salt. In that case  purification is needed and that can be done based on the nature  of other metal salts.

Maybe the better procedure should be to add only water to convert CaO to Ca(OH)2, and then slowly add dilute HNO3. Both reactions are exothermic, so you have to be cautious. After filtration it should be best to put solution to slowly crystallize, so you will obtain nice crystals of high purity. 

I think that the answer of Mr. Sarkar is more correct, just use a dilute HNO3 and control pH value. You will not get anhydrous Ca(NO3)2 using this procedure, but you will be able to measure water content in the final product by Ca2+ titration.