Lithium dihydrogenphosphate (LHP) needs to be dehydrated to be safely applied for the melt casting process to produce lithium iron phosphate (LFP). The dehydration reaction consists of several consecutive melting, oligomerization, and crystallization steps resulting in a solid product stuck to the reaction vessel at around 400 degrees C. Here we applied an electrical shell-heated rotary kiln containing grinding media (ball-mill rotary-kiln, BaMRoK) to dehydrate LHP at 400 degrees C and recover the ground product without needing any extra processing. The bulk convective heat transfer coefficient of the kiln has been calculated in the presence of the grinding media and the temperature profile has been modelled using COMSOL Multiphysics. The kinetic model of the reaction from thermogravimetric analysis (TGA) and the thermal profile suggest that the dehydration reaction mostly happens on the internal surface of the BaMRoK wall.