###### Abstract  
This manuscript describes molybdenum recovery from copper Pregnant Leaching Solutions (PLSs) in the copper oxide mining industry with high contents of chloride ions. This product was recovered from the copper leaching pond solutions of the Chilean National Copper Mining Corporation (CODELCO) using the ion exchange process. This process recovered molybdenum from initial Mo concentrations of 50 mg/L using two different anion--exchange resins. The first experiments, with 1 g/L Cl\({}^{-}\), achieved recovery yields of 90% and molybdenum concentrates as CaMoO\({}_{4}\). However, the process was permanently halted because of the early saturation of the ion exchange resins given by high chloride concentrations (10 g/L Cl\({}^{-}\)) of the original copper PLS and the significant reagent consumption given by the low adsorption capacity. Static studies were developed to determine the adsorption isotherms, followed by continuous molybdenum recovery tests. The Langmuir adsorption parameters were determined as a function of the chloride concentration, giving absorption capacities from 180 to 250 mg Mo/gram of resin and recoveries from 63% to 90%. The breakthrough values for the DOWEX and Lewatit resins for chloride contents of 10 g/L were 180 and 245 BV, respectively, while for 1 g/L, these values were 620 and 890 BV. This allowed obtaining elution solutions of 890 mg Mo/L for the DOWEX resin and 1000 mg Mo/L for the Lewatit resin. molybdenum; copper PLS; ion exchange; Langmuir adsorption +
Footnote †: journal: Applied Sciences  
**Citation:** [PERSON]; [PERSON]; [PERSON]; Molybdenum Recovery from the Copper Hydrometallurgical Extraction Route with High Content of Chloride Ions Using the Ion Exchange Technique. _Appl. Sci._**2024, 14, 7477. [[https://doi.org/10.3390/app14177477](https://doi.org/10.3390/app14177477)]([https://doi.org/10.3390/app14177477](https://doi.org/10.3390/app14177477))
Molybdenum production procedures primarily involve the production of molybdenum powder and molybdenum byproducts from chemical purification operations. Figure 1 depicts the stages of molybdenum powder production, which include roasted molybdenum to obtain molybdic acid and ammonium molybdate as raw materials after calcination to obtain molybdenum trioxide (MoO\({}_{3}\)). Then, molybdenum powders are obtained through a reducing agent, usually hydrogen [9; 10; 11]. Figure 1 depicts the specific production processes involved in the production of molybdenum. After the dissolution of molybdenum concentrates, ion exchange and solvent extraction can be employed to separate or purify metal ions present in aqueous solution [12; 13; 14; 15; 16]. In these two processes, each has its advantages and disadvantages over the other. Solvent extraction is highly selective and efficient for extracting Mo from sulfuric acid leach solution. However, owing to the co\(-\)extraction of impurities, such as Co, Ni, and Fe, Mo separation is inefficient in extraction alone, requiring in some cases previous acid washings [17]. Although the loading capacity of ion exchange for metal ions is low, the operation of ion exchange is simple and producing Mo with high purity is possible [18]. Hence, when the concentration of Mo in sulfuric acid solution is not high, ion exchange resins can selectively load Mo from the solution in the presence of other metals. Therefore, the ion exchange processes are the best way to recover molybdenum from aqueous solutions. In the pH range 1-6, the molybdenum ions exist as polyanions, which are bigger than the monomeric anions. That is why it is convenient to use highly permeable anion exchangers for the ion exchange recovery of molybdenum. Such sorbents are the porous and microporous resins [19; 20]. In general, quaternary amine\(-\)based resins are used to recover anionic species and they have the following selectivity: SO\({}_{4}\)\({}^{2-}\) > NO\({}_{3}\)\({}^{-}\) > Cl\({}^{-}\) > HCO\({}_{3}\)\({}^{-}\) > OH\({}^{-}\) > F\({}^{-}\)[21; 22].