<p>The tailings dam of the Chadormelo iron ore processing plant contains rare earth elements including major minerals such as hematite (Fe₂O₃), quartz (SiO₂), fluorapatite (Ca₅(PO₄)₃F), calcite (CaCO₃), goethite (FeO(OH)), and dolomite (CaMg(CO₃)₂), so that about 83.84% of the total sample weight is composed of iron oxides with 41.52%, carbonate minerals (calcite and dolomite) with 22.12%, and quartz with 20.2%. The total grade of rare elements in the sample is 1068.57&#xa0;ppm, containing 84.61% light rare elements and 15.39% heavy rare elements. SEM studies showed that monazite ((Ce,La)PO₄), xenotime (YPO₄), and apatite (Ca₅(PO4)₃(OH,F,Cl)) minerals contain rare elements. Therefore, the leaching method with nitric acid was used to dissolve rare elements, and parameters such as nitric acid concentration, solid pulp percentage, time and temperature were investigated and optimized using the experimental design method. In addition, the optimal conditions were determined as nitric acid concentration value of 50%, solid pulp percentage value of 25%, time value of 2&#xa0;h and temperature of 40°C. A leaching recovery percentage of 46.34% was obtained under the above conditions. The resistance of the monazite mineral was identified as one of the main reasons for the low recovery of rare elements by nitric acid. Therefore, to increase the recovery of rare elements, the pre-alkaline processing method was proposed before leaching with nitric acid. First, alkaline leaching was performed under optimal conditions (sodium hydroxide concentration 70&#xa0;g/L, temperature 160°C, time 3&#xa0;h and pressure 6 atmospheres), and then leaching with nitric acid was used. Using the pre-alkaline processing increased the leaching recovery percentage about 21.34%, and the leaching recovery percentage using both alkaline and nitric acid increased from 46.34% to 67.68%.</p>