Investigation and optimization of tin electrorefining in hydrochloric acid solutions

Abstract

High-tin containing soldering waste material could be recycled close to its origin on a flexible scale by electrolytic refining in pure hydrochloric acid-tin-chloride solutions. This method, offering potentially low costs, may become feasible by overcoming the difficulties of solution stability, electrolytic efficiency and deposit morphology. The tendency of the Sn(II) oxidation and precipitation can be overcome by properly controlling the concentration of the main components and the ratio of Sn(IV)/Sn(II) in the electrolyte solution. The virtual cathodic current efficiency can be increased above 90 % by assuring the dominance of Sn(II) species and optimising the composition of the electrolyte solution, the applied apparent current density and the parameters of the periodical current reversal. In the selected medium, the formation of chloro-complex ionic species may offer a beneficial level of natural inhibition. Organic additives exert no beneficial effect on any of the electrolysis characteristics. Applying a short cycle periodic current reversal technology is efficient in improving the morphology of the cathodic deposit. The loose structure of deposited metal requires special cell arrangement and care during operation. Electrolyte circulation does not affect current efficiency significantly. It should be applied in practice for the control of composition. The attainable purity is close to 99.99 %, which greatly surpasses the technical standards.

Electrochemical mechanism of tin membrane electro‐deposition in chloride solutions

“…The acidic electrolytes in the main form of tin(II) sulphate, sulphonate or fluoroborate assure hydrolytic stability and improve conductivity, but tin whiskers are formed without any additives owing to extremely small electrochemical reaction overpotential and the rapid reduction reaction rate of Sn 2+ . Specifically, considering the economic disadvantages of alkali stannate or sulphuric acid – cresylic phenylic sulphonic acid baths, Kekesi et al proposed the application of HCl‐SnCl 2 solutions for tin electrorefining . The anodes were cast from tin scrap and the starting cathode was a masked copper plate which was coated with a compact layer of tin deposited by pre‐electrolysis.…”

“…Specifically, considering the economic disadvantages of alkali stannate or sulphuric acid -cresylic phenylic sulphonic acid baths, Kekesi et al proposed the application of HCl-SnCl 2 solutions for tin electrorefining. 8,9 The anodes were cast from tin scrap and the starting cathode was a masked copper plate which was coated with a compact layer of tin deposited by pre-electrolysis. The anodic dissolution of tin and the cathodic reduction of ions were achieved with an electric current.…”

Study On The Electro-Refining Of Tin In Acid Solution From Electronic Waste

“…It is generally known that the alkaline electrolyte solution is not widely used for electro-refining process in industry owing to its high temperature, high solubility of impurity, but the homogeneous and dense deposited film could be achievable on the surface [5]. Meanwhile, the acid electrolyte solution for tin electro-refining process is widely used in industry with the advantages of low temperature process and low solubility of impurities but the sludge and slime occurred on surface of anode, which could lead to gradual decrease of current efficiency [6]. Organic additives in acid electrolyte are necessary to obtain smooth and dense tin films because tin of cathode was electrodeposited in the shape of needles, whiskers and dendrites [7,8].…”

Leaching Behavior of the Anode Slime Generated by the Electrorefining of Sn-Ag-Cu Alloys

“…The wave soldering technique is associated with the generation of dross, containing the valuable tin and silver metals. By re-melting the primary dross and after skimming, the molten metal can be cast into anodes and pure tin can be recovered by electrorefining in HCl media [2,3]. Due to the higher electrode potentials, silver and copper are expected to accumulate undissolved in a slime layer formed at the anode surface containing a large amount of metallic particles fallen out of the anode substrate as a result of uneven dissolution.…”

“…The amount of the metallic phase strongly depends on the conditions of anodic dissolution. At high anodic potentials, associated with high anodic current densities, dissolution results in the generation of Sn(IV) species which may in turn react with the metallic particles of the thick slime layer [3,4]:…”