Thermodynamics of chemisorption of sulfur from thiocyanate on nickel during electrochemical passivation

An alternative to cyanide leaching of waste activated carbon ash for gold and silver recovery via synergistic dual-lixiviant treatment

“…It also has a high affinity for thiocyanate (Ksp for CuSCN(s) formation = 5.75 x 10 12 [40]). Thiocyanate is known to readily adsorb and deposit sulfur on a variety of metallic surfaces, such as Cr, Fe and Ni [56,57]. Additionally, Sn thiourea and thiocyanate complexes are readily formed in aqueous, acidic conditions [58,59], although nothing is reported as to their interference in Ag and Au leaching.…”

Chemisorption model of electrochemical passivity of metals and thermodynamic calculation of the flade potential of metals Ni and Cr taking into account their surface Gibbs energy

“…Using the example of a reaction between KSCN thiocyanate and nickel in a 0.5 M H 2 SO 4 aqueous solution, it was shown [12] that, in this case, two com petitive processes occur: the formation of a passivation film of NiO …”

“…The experimental part of the study is focused on the relationship between the calculated Flade potential of nickel and the critical points in the anodic curves of passivation and depassivation of nickel in a standard solution of 0.5 M H 2 SO 4 . In addi tion, the nature of the chemisorption of water mole cules on nickel is discussed using the results of [12] regarding the competitive chemisorption of sulfur on nickel in the same solution with KSCN thiocyanate additives.…”

“…On the other hand, defining the autoadsorption energy of the adatoms as = (a nega tive value) and using (10), we obtain the relationship (12) in which, in the absence of competing atoms or mole cules, the autoadsorption energy of the intrinsic metal atoms is entirely determined by the surface energy of the metal.…”