A process for the detanning of chrome leather wastes utilising tannery effluents
- Authors: Glaum, Deanne Melanie
- Date: 1994
- Subjects: Tanneries -- Waste disposal , Recycling (Waste, etc.) , Leather
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4029 , http://hdl.handle.net/10962/d1004089 , Tanneries -- Waste disposal , Recycling (Waste, etc.) , Leather
- Description: The considerable volume of chromium-bearing wastes generated during the process of leather tanning, exacerbated by the potential for trivalent chromium in the wastes to be oxidised to the toxic hexavalent state, has created a major waste disposal dilemma for the tanning industry. While methods are available for the safe and effective treatment of residual chrome-tanning liquors, little has been done to address the issue of the chrome-bearing solid wastes. Given the increasingly stringent environmental compliance standards facing tanneries, unless an appropriate treatment process is developed in the immediate future, the continued use of chromium as a tanning agent could be compromised. Recent investigations have demonstrated the potential of heated alkaline conditions for dechroming these solid wastes. This study expanded upon these considerations and examined the feasibility of utilising the highly alkaline tannery waste effluents as cost-effective, substitute alkaline media. The three effluents considered in this study, classed as lime sulphide liquors, were shown to be capable of dechroming wet blue shavings, with resultant separation of the solid wastes into a protein and a concentrated chromium product. The solubilised protein product contained low chromium concentrations which comply with legal discharge limits. The precipitated chromium product offers opportunity for reutilisation in the tannery. A novel industrial-scale treatment process, based on these investigations, indicated the process to be capable of treating the quantity of shavings produced on a daily basis by a medium to large scale tannery. Application of this method for the dechroming of other chrome-tanned solid wastes was also shown to be feasible.
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- Date Issued: 1994
A study on white leather tannage
- Authors: Williams-Wynn, D A
- Date: 1950
- Subjects: Leather , Tanning , Aluminum sulfate , Mineral tanning
- Language: English
- Type: Diploma theses , text
- Identifier: http://hdl.handle.net/10962/193713 , vital:45389
- Description: As has been noted in the previous section little or no complex formation occurs with either formate or acetate except possibly above pH 9*0 or so. These anions do not stabilise the aluminium solutions to precipitation - they may* however, be of value in controlling pH, as solutions of these salts buffer strongly in the region pH 4 to 5. The other salts, lactate, tartrate and citrate all show tendencies to complex formation though the degree to which this occurs varies with the anion. The complexes formed by lactate at high pH must be very unstable because on the addition of acid the pH corresponds to the calculated blank. Below pH 9.0 however, the curves deviate quite considerably showing that more acid must be added to reach a certain pH value than is required by the blank. This means complex formation has occurred with loss of -COGH groups. In this system too, buffering is apparent. The same is true of tartrate but this salt is not as efficient a buffering agent. This is probably due to the fact that the excess tartrate is not available as a buffer as it is precipitated as the acid salt which is only sparingly soluble. Citrate on the other hand must form very stable complexes, the effect of which is apparent at even very high pH values. In other words, addition of strong acid liberates free -GOGH groups which are immediately incorporated in the complex. This evidently does not occur with lactate or tartrate until lower pH values are reached. The ratio of lactate and citrate to aluminium appears to have some influence on the degree of masking as greater complex formation is found to occur at the higher ratio levels. Tartrate on the other hand apparently has a fixed complex forming capacity between 1 and 4 mols/mol aluminium, since the same deviation from the blank was observed irrespective of which ratio of the masking agent to aluminium, was employed. However, at ratios of less than 1 mol tartrate/mol aluminium, deviations from the blank were reduced and less stabilisation occurs as evidenced by the formation of precipitates containing aluminium under these conditions. In view of these facts it may be suggested that 1 mol tartrate combines with 1 mol aluminium to form a complex containing equimolar proportions of aluminium and tartrate. The effect of boiling apart from one or two exceptions always has the same effect, i.e. a shift to the acid side of the curve. Free acid must have been liberated which is an indication that olation might have occurred. In the lactate and citrate series dilution appears to reduce the complex forming capacity of these ions but tartrate is unaffected. Thus it would appear that the tartrate complex is more stable than those formed by lactate. Citrate stabilises aluminium solutions with fewer equivalents than tartrate, but the complex does not contain a constant ratio of masking agent to aluminium further quantities of tartrate cannot enter the complex even in the presence of large excess of the anion probably due to the effect of steric hindrance. , Thesis (Dip) -- Leather Industries Research Institute, 1950
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- Date Issued: 1950