PbCO3 is essentially insoluble in water. NaCl is very soluble in water. Adding water to a mixture of PbCO3 and NaCl will dissolve the NaCl but not the PbCO3. The complicating factor is that PbCl2 can form also, although in small amounts. But PbCl2 is quite soluble in hot water. So, add water, heat to near boiling in order to dissolve any PbCl2 that has formed, filter, PbCO3 will be in the residue and any PbCl2 and NaCl will be in the filtrate.
