Copper cyanide adsorption

The SG(l)-TEPA-propyl/Copper Cyanide Adsorption Process.246... 

Bozzini, B., D Urzo, L., Mele, C. and Romanello, V. (2008) A SERS investigation of cyanide adsorption and reactivity during the electrodeposition of gold, silver, and copper from aqueous cyanocomplexes solutions. The Journal of Physical Chemistry C, 112, 6352-6358. 

Anstice, P.J.C., and Alder, J.F., The effect of sulphur dioxide exposure under controlled environmental conditions on the challenge performance of copper- and chromate-impregnated active carbon against hydrogen cyanide, Adsorpt. Sci. Technol., 15(7), 531-540 (1997). 

Remove Pb(ll) to less than 1 ppm and stable for 20 adsorption/ stripping cycles Simultaneous removal and separation by selective stripping Recover and recycle copper cyanide from cyanide waste solutions... 

The adsorbent SG(l)-TEPA-propyl is useful in adsorbing anionic copper cyanide complexes from electroplating solutions. Modeling this anionic adsorption phenomena requires the description of copper cyanide ion speciation in the aqueous solution, the acid-base characteristics of the adsorbent, and the complexation reactions between the copper cyanide anions and the protonated ligand sites. Details can be found elsewhere [5,30],... 

Copper cyanide complexes are usually present as monovalent (Cu(CN)2 ), divalent (Cu(CN)3 ), and trivalent (Cu(CN)4 ) species in aqueous solutions, as shown in Figure 7.4. Computations for copper cyanide speciation show that for ratios of total copper cyanide to total copper greater than 16, speciation at any given pH does not depend on the [CN]j/[Cu]x ratio. The solution pH, however, greatly affects the speciation of complexes (see Figure 7.4). The fraction of monovalent species decreases whereas the fraction of the divalent species increases as pH increases. Concentrations of trivalent species are negligible below pH 7.5. These results show the need to consider pH dependency of speciation in the adsorption isotherm expression. 

The adsorption mechanism of copper cyanide complexes can be described as follows ... 

To model the adsorption of copper cyanide complexes, the multicomponent Langmuir isotherm can be modified to correlate the aqueous phase speciation and the basicity of the ICAA. The available protonated sites on the ligands attached to the surface also can be assumed to be a function of pH. 

The adsorption of trivalent copper cyanide from solution can be neglected when the pH is lower than 8 because it exists in very small amounts. If we assume that all the protonated sites can adsorb copper cyanide species, and the effect of ionic strength can be neglected in the adsorption processes, the modified multicomponent Langmuir isotherm can be written for total amount adsorbed q as follows ... 

Adsorption isotherms were generated for the copper cyanide complex adsorption at three pH values, and the Langmuir constants and geometrical factor were found to have values of Kj = 2.43, L/mmol, K2 = 3.95 L/mmol and/= 0.40. A comparison of the experimental values and those calculated with the model and obtained parameters is given in Figure 7.22. 

FIGURE 7.22 Adsorption isotherms of copper cyanide complexes at three different pH values. Symbols represent experimental data for the different pH conditions and solid lines represent the the modified multicomponent Langmuir Equation (7.13). (Reproduced from J. S. Lee, N. V. Deokar, and L. L. Tavlarides. Ind. Eng. Chem. Res. 37 2812-2820,1998. With permission.)... 

It was observed that the extraction rate of copper-cyanide complexes on SG(1)-TEPA-propyl is too rapid to measure due to fast kinetics and pore diffusion (small particles). Accordingly, the adsorption behavior can be easily modeled using the equilibrium model of Section 7.4. 

The results of the breakthrough curve experiments and the model computation are shown in Figure 7.25. The experimental result shows that the adsorption of copper cyanide complexes on SG(l)-TEPA-propyl is controlled by equilibrium because the slope of the curve at the breakthrough point is a sharp, step-like response. This response suggests that there are no film resistances at the particle surface, fast diffusion of copper cyanide complexes through the pores, and fast adsorption reaction on the functional sites. Hence, the developed equilibrium model weU represents the experimental data since it is developed based on the assumption of equilibrium... 

J. S. Lee. Adsorption of Copper Cyanide on Inorganic Chemically Active Adsorbents, M.S. Thesis, Syracuse University, 1997. 

In this work, the waste brewery yeast and Aspergillus niger were used for the adsorption of lead, copper and cadmium, and their cyanide complexes. Biosorption equilibrium was studied in a batch reactor with respect to pH, initial concentration of heavy metal and metal-cyanide complex. Biosorption equilibrium over the temperature range of 288K - 308K was investigated and the biosorption heat was evaluated. 

All these processes are very expensive for the purpose of removing a small amount of cyanide. The adsorption/oxidation process with PAC and copper could be easily incorporated into existing biological treatment systems however, the concern of copper toxicity in the final effluent makes this process undesirable. 

Depressants (or deactivators) are chemicals that ensure that undesired particles remain hydrophilic and therefore do not get floated. Conversely to the activation of zinc sulfide by copper ions above, zinc ions from zinc sulfate act as a depressant for zinc sulfide. Another example is the use of cyanide to complex with copper and prevent adsorption of collectors in the flotation of base-metal sulfides with xanthates. There are many other depressants but they tend to be quite specific to one of a few types of minerals. In some cases, such as some uses of cyanide as a depressant, the mechanism of depressant action remains unclear. 

Other metals, such as copper, nickel, or silver, have been used as electrode materials in connection with specific applications, such as the detection of amino acids or carbohydrates in alkaline media (copper and nickel) and cyanide or sulfur compounds (silver). Unlike platinum or gold electrodes, these electrodes offer a stable response for carbohydrates at constant potentials, through the formation of high-valence oxyhydroxide species formed in situ on the surface and believed to act as redox mediators (40,41). Bismuth film electrodes (preplated or in situ plated ones) have been shown to be an attractive alternative to mercury films used for stripping voltammetry of trace metals (42,43). Alloy electrodes (e.g., platinum-ruthenium, nickel-titanium) are also being used for addressing adsorption or corrosion effects of one of their components. The bifunctional catalytic mechanism of alloy electrodes (such as Pt-Ru or Pt-Sn ones) has been particularly useful for fuel cell applications (44). 

Other factors, of course, come into play in an actual plating bath. For example, plating from an acid bath takes place at around 0.3 V, NHE, whereas in a cyanide bath, copper is deposited at a much more negative potential. The former occurs at a positive rational potential, while the latter occurs at a negative rational potential. This affects the choice of additives and their adsorption characteristics. Also, the values of ( ) and d( ) /d( ) may be different in the two cases. The foregoing example is not intended to be a quantitative interpretation of the benefits of cyanide baths, but rather an illustration of how considerations of a rather fundamental nature can assist in solving applied problems. 

The adsorption of CN on a polycrystalline copper electrode has been studied experimentally by Lee et al. [116], Since copper oxidizes more readily than gold and silver, the results depend strongly on the cyanide concentration. At low cyanide concentration in solution (2x 10 M), a potential dependent band between 2084 and 2120cm was assigned to the linearly adsorbed CN ion (Fig. 33, p. 172). 

Two representative examples of this behavior are reflected in two distinct different chemical systems, namely (a) copper deposition from an acid sulfate electrolyte containing the co-inhibitors PEG-C1 and a bi-functional catalytic species SPS-C1 [12, 136, 243, 264] and (b) silver deposition from a cyanide electrolyte where inhibition is provided by adsorption of silver cyanide species and catalysis is achieved through adsorption of selenocyanate, SeCN [72-75]. Similar behavior is evident in some electrolytes used for the deposition of bright soft gold films [121, 180, 255-261, 267]. 

Amperometric techniques are very useful for detecting analytes that have been separated by chromatographic means but have no chromophores or other easy means of detection. Adsorptive stripping voltammetry (ASV) can be used for the direct sensitive analysis of metals in many types of sample matrix. For example, ASV has been used to determine cadmium, lead and zinc in urine, copper and bismuth in human hair tin in fruit juice, zinc and copper in fish and lead in gunshot residue. Stripping analysis can also be used for other applications such as determining flavanols in wine °, inorganic compounds such as cyanide and pharmaceuticals. ... 

Fleischmann et al [22] compared benzotriazole and 2-mercaptobenzoxazole as inhibitors of copper corrosion in KCl solutions containing low concentrations of cyanide. Benzotriazole proved to be an ineffective inhibitor in cyanide media, while 2-mercaptobenzoxazole remained effective. SERS showed that cyanide, revealed by a broad band centred at 2090 cm displaced benzotriazole from the Cu surface, whereas 2-mercaptobenzoxazole displaced adsorbed cyanide. A synergetic inhibition of Cu corrosion by benzotriazole and benzylamine, both in chloride and chloride/cyanide media, was also shown [22]. As SERS showed that benzylamine had not been adsorbed, its beneficial effect was ascribed to an improved film formation. Subsequent 4or measurements showed that benzotriazole, MBO, 2-mercaptobenzothiazole and 2-mercaptobenzimidazole were all effective inhibitors of copper corrosion in neutral chloride solutions, but the inhibition efficiency of benzotriazole was decreased at pH 1-2 [23]. SERS spectra showed that, at pH 7, benzotriazole and its anionic form were coadsorbed and Cl was excluded from the interface. However, at pH < 2 undissociated benzotriazole and CH were coadsorbed, such that Cu underwent corrosion. In contrast, the anion from 2-mercaptobenzothiazole was the only adsorbed species at pH between 7 and 2 only at pH 1 was the neutral 2-mercaptobenzothiazole molecule detected. Competitive adsorption experiments showed that the inhibitive action of benzotriazole and 2-mercaptobenzothiazole in neutral/acid media could be explained in terms of adsorption strength. 

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