You may try 2eq piperazine x1HCl in EtOH (add conc. HCl to a suspension of piperazine in EtOH, this gives a clear solution). Then slowly add the iodide. Works best for chlorides since the dihydrochloride of excessive piperazine precipitates.

ok... I've tried this procedure, and a yellow solid was formed. However, the product seems to stay in the aqueous phase during the work-up... How can I obtain it from the aqueous solution without extract the piperazine?

many derivatives can be extracted at pH 11-12 with CHCl3 (not CH2Cl2). Beforehand it is important to remove most of the EtOH since without phase separation the CHCl3 may react exothermal. Some piperazine will also be extracted an can be removed by sublimation under reduced pressure or repeated evaporation of water. If the precipitated dihalide is free of product, there should be not too much piperazine in the aqueous phase.