Brines coming from salted lakes such as that at the Atacama desert in Chile produce by-products or wastes which today are stored in the nearby from the production areas. Bischofite is one of those by-products, and therefore, its composition may vary from batch to batch. Because bischofite has been identified as a good candidate to be used as phase change material (PCM) for latent heat thermal energy storage, the influence of the variation of bischofite composite with its main impurities in this potential used needs to be evaluated. The main impurities of bischofite are the cations sodium, potassium and lithium and the anions chloride and sulfate. The results of this investigation established that the presence of KCl and NaCl in bischofite (up to 5 wt%) does not affect its use as PCM, because its melting enthalpy and temperature do not vary significantly. It is interesting that small contents of LiCl in bischofite do not change significantly its melting enthalpy but decrease the melting temperature. Such change may enable the usage of this material as PCM in other applications at lower temperatures.