Recovery of Tantalum and Manganese from Epoxy-Coated Solid Electrolyte Tantalum Capacitors through Selective Leaching and Chlorination Processes

Electronic products are ever growing in popularity, and tantalum capacitors are heavily used in small electronic products. Spent epoxy-coated solid electrolyte tantalum capacitors, containing about 22 wt.% of tantalum and 8 wt.% of manganese, were treated with selective leaching by hydrochloric acid and chlorination after removing the epoxy resin, and the products converted, respectively, to Mn(OH)2 and TaCl5. The effects of acid type, acid concentration, liquid–solid ratio, and reaction time were investigated to dissolve the manganese. The optimal selective leaching conditions were determined as 3 mol/L of HCl, 40 mL/g at 25 °C for 32 min. Next, residues of selective leaching after washing and drying were heated with ferrous chloride to convert to pure TaCl5. Mixing 48 wt.% of chloride and 52 wt.% of residues for a total of 5 g was conducted to complete the chlorination process in the tube furnace at 450 °C for 3 h. A total of 2.35 g of Ta was collected and the recovery of Ta achieved 94%. Finally, Mn(OH)2 and TaCl5 were separated and purified as the products.

Selective Leaching of Molybdenum from Bulk Concentrate by Electro-Oxidation

This paper proposes selective leaching of molybdenum from Mo/Cu complex bulk concentrates in a 5 M NaCl solution using the electro-oxidation method. Here, the effects of several factors such as pH, pulp density, current density, and temperatures were investigated. A higher leaching yield of Mo increased with increasing pH from 5 to 9 and decreased with increasing pulp density from 1 to 10%. A rise in current density did not help enhance Mo, and the elevating temperature did not always result in a higher leaching yield. Application of ultrasonic led to higher leaching yield of Mo. Ninety-two percent of leaching yield was obtained upon leaching of Mo in 5 M NaCl at 25 °C, pulp density of 5%, and the current density of 0.292 A/g under ultrasonic irradiation with a power of 27 kW. The resultant residue mainly consisted of chalcopyrite.

Dissimilar Metal Solution from Solid Alloys as Observed for Steels and Nickel‐Based Alloys in the Presence of Lead‐Based Liquid Alloys or Liquid Tin

The solution of elements from metallic alloys is analyzed, notably the initial stage characterized by solution in proportion to the alloy composition and subsequent selective leaching of alloying elements. For the latter stage of the process, characteristic features of the originating depletion zone are derived for different formation mechanisms. The results are compared with observations for steels and nickel-based alloys after exposure to lead-based liquid alloys or liquid tin, and, where possible, the prevailing mechanism is identified. Furthermore, the influence of dissolved oxygen and formation of intermetallic compounds are addressed.

Effect of Fe2O3 Content and Acid on the Leaching Behavior of Phosphorus from Dephosphorization Slag

Dephosphorization slag contains considerable quantities of valuable components, such as P2O5 and FeOx. To recover P from dephosphorization slag, selective leaching has been adopted to separate the P-concentrating mineral phase. In this study, the effect of Fe2O3 content in slag and acid on the leaching behavior of P from dephosphorization slag was investigated. It was found that a higher Fe2O3 content in slag resulted in a higher P2O5 content in the C2S–C3P solid solution. Increasing the Fe2O3 content in slag promoted the dissolution of P and simultaneously suppressed the dissolution of other elements, facilitating the selective leaching of P. In the hydrochloric acid solution, more than 81% of P could be dissolved from dephosphorization slag at pH 4, and the dissolution ratio of Fe was nearly zero, achieving excellent selective leaching. Although better selective leaching was also realized in the citric acid solution at pH 5, hydrochloric acid was considered the appropriate leaching agent from the perspective of leaching cost. Through selective leaching, almost all the C2S–C3P solid solution was dissolved from dephosphorization slag, and the Fe-bearing matrix phase and magnesioferrite remained in the residue. The residue with low P2O5 content can be reutilized in ironmaking or steelmaking processes.

Selective Leaching Trace Elements from Bauxite Residue (Red Mud) without and with Adding Solid NH4Cl Using Microwave Heating

Bauxite residue (red mud), which is an industrial byproduct, contains valuable trace elements. Solid NH4Cl was used as a chlorinating agent during the microwave heating of red mud to convert trace elements into soluble metal chloride. Red mud was heated using microwave ovens under various conditions (i.e., with the addition of solid NH4Cl and with a range of microwave output powers and microwave heating times). Leaching tests were then conducted using deionized (DI) water on the microwave-heated red mud to leach trace elements from red mud. V, Cr, and As were selectively leached from the microwave heated red mud slurry (30% water content), whereas Mn, Cu, Co, Ni, Zn, and Pb were selectively leached from the microwave-heated red mud with the addition of solid NH4Cl. The oxides of V, Cr, and As in red mud could be transformed into metal chlorides by chlorination, which are insoluble in water, or could be easily volatilized when red mud was microwave-heated in the presence of solid NH4Cl. On the other hand, the oxides of Mn, Cu, Co, Zn, Ni, and Pb in red mud could be heated rapidly by microwave irradiating, resulting in metal chlorides in the presence of solid NH4Cl. Those metal chlorides are relatively soluble in water, leading to higher leaching efficiency for microwave-heated red mud with the addition of solid NH4Cl. Experimental results suggest that trace elements from red mud can be selectively leached by microwave heating of red mud without or with the addition of solid NH4Cl.

Comparative Study for Selective Lithium Recovery via Chemical Transformations during Incineration and Dynamic Pyrolysis of EV Li-Ion Batteries

Selective leaching of Li from spent LIBs thermally pretreated by pyrolysis and incineration between 400 and 700 °C for 30, 60, and 90 min followed by water leaching at high temperature and high L/S ratio was examined. During the thermal pretreatment Li2CO3 and LiF were leached. Along with Li salts, AlF3 was also found to be leached with an efficiency not higher than 3.5%. The time of thermal pretreatment did not have a significant effect on Li leaching efficiency. The leaching efficiency of Li was higher with a higher L/S ratio. At a higher leaching temperature (80 °C), the leaching of Li was higher due to an increase in the solubility of present Li salts. The highest Li leaching efficiency of nearly 60% was observed from the sample pyrolyzed at 700 °C for 60 min under the leaching condition L/S ratio of 20:1 mL g−1 at 80 °C for 3 h. Furthermore, the use of an excess of 10% of carbon in a form of graphite during the thermal treatment did not improve the leaching efficiency of Li.