Abstract
Leather processing requires substantial inputs of energy, water and chemicals. Additionally, it generates significant amounts of liquid and solid waste, severely impacting the environment. Processing 1 Mg of raw hides yields up to 600–700 kg of waste, considerable amounts of which are solid tannery waste. Such waste contains chromium (Cr) compounds, which are commonly used as tanning agents. This paper reviews solid tannery waste treatment technologies, with emphasis on waste incineration in a specially designed experimental tunnel incinerator. Three different types of tannery waste were subjected to tests: trimmings, shavings and buffing dust. As the research revealed, the process can be applied to all types of solid tannery waste. Moreover, it enables the reuse of the heat of the process and results in a Cr concentrate in the process residues. The conducted analyses (carbon, hydrogen and nitrogen elemental analysis; inductively coupled plasma optical emission spectroscopy; powder X-ray diffraction) proved that there is no or little organic content in the obtained residual ash, which contains up to 53.1%(w/w) Cr in the form of Cr (III) oxide. Such material may be used as a Cr ore substitute in the chemical or metallurgical industries.
Highlights
The tanning industry is considered one of the most environmentally unfriendly industrial activities [1]
It was the highest in the case of incineration of trimmings (77.6%(w/w)) and exceeded the results presented by Kluska et al [29,30], who observed the Cr2 O3 share in the ash after incineration of shavings pellets in the range
The presented results demonstrate that the Tanned solid tannery waste (TSTW) incineration processes in a tunnel incinerator system are practically complete and the obtained ash (amounting to approx. 7.4%–10.5%(w/w) of incinerated waste depending on waste type input) contains mostly Cr2 O3 and slight amounts of organic content
Summary
The tanning industry is considered one of the most environmentally unfriendly industrial activities [1]. Namely processing raw hides into a useful product called leather, requires a considerable material and energetic input (process water, chemicals, process heat) and generates significant amounts of wastewater, air pollution and solid waste as an output [2,3]. There are different types of solid tannery waste, depending on the process stage during which the waste is generated They can be divided into three main groups [5,6,7]: Untanned solid tannery waste (USTW), such as trimmings (unused pieces of hides) or fleshings (non-leather tissues that have been mechanically scraped off). This waste is prone to biologically-mediated decay
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