Potassium is an essential ion for plant nutrition, usually supplied in the form of chlorides and sulphates. According to Brazilian availability and demand of agriculture fertilizers, the importation of compounds carrying this chemical element is mandatory in order to fulfil the huge demand for this nutrient. Thus, initiatives looking for alternative sources of potassium become increasingly interesting and economically attractive. A potential route is associated with the sulfuric acid digestion of glauconite bearing greensands and sequential unit operations in order to recover aluminium, iron, magnesium and potassium compounds. In the context of this chemical process, the potassium alum (KAl(SO4)2) appears as a relevant intermediate product, which allows the selective recovery of potassium sulphate (K2SO4) and aluminum oxide (Al2O3) through thermal decomposition followed by solubilization in water and filtration. Based on what was said, the present work investigates the kinetics of potassium alum dodecahydrate (KAl(SO4)2.12H2O) decomposition with and without the presence of charcoal, which acts as a reducing agent. Additionally, the current work proposes a novel mathematical model to describe the weight loss as a function of time for both processes (with and in absence of charcoal). Thermogravimetric analyses (TGA) were conducted under inert atmosphere (nitrogen) and using different heating rates (10, 15 and 20 ? min-1). Given the low required computation time, less than 1 s simulates 160 min of reaction, the proposed model can be used to monitor and control mass compositions at industry.