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Author(s): M. A Fonseca
Rui A. R. Boaventura
Title: Chromium precipitation from tanning spent liquors using industrial alkaline residues: A comparative study
Issue Date: 1998
Abstract: Chromium precipitation from spent tanning liquors using industrial alkaline tailings is described and removal efficiencies are compared with those obtained with traditional chemicals as NaOH, CaO and MgO: (i) using steelmaking dusts at dosages up to 70 gl-1 residual Cr remains 3.7 mgl- 1. Moreover Cr and mainly Pb are partially leached by the spent tanning liquor, therefore limiting the use of this industrial residue as Cr precipitant; (ii) a dosage of 80 gl-1 (dry basis) of chemical sludge from a water treatment plant results in a removal efficiency of 99.97% Cr and residual Cr2 mgl-1 under experimental conditions that include stirring at 100 rpm for 1 h and settling for 23 h. Sedimentation time may be reduced to 2 h if stirring is extended to 2 h. Resulting sludge volume is about 400 ml 1- 1. However, during Cr precipitation, A1 is leached from the added product up to about 40 mg A1 per litre of supernatant; (iii) precipitation using acetylene production sludge only requires a dosage of 16 gl-1 (dry basis) to remove 99.96% Cr after stirring for 1 h and settling for 2 h. The soluble Cr concentration in the clarified effluent is 2 mg 1-1 and the sludge volume about 500 ml 1-1. This Cr level can also be achieved at a dosage of 14 g 1-1, provided the stirring time is increased to 3 h; (iv) these results are comparable with those using either CaO or MgO at similar dosages (14 and 18 mg l-1, respectively); and, (v) NaOH at dosages between 6.4 and 14 gl-1 proved to be not sufficiently effective for Cr precipitation. Although removal efficiencies up to 99.9% are achieved, residual Cr is always above 8.7 mg 1-1. Additionally, the resulting sludge is not very dense, thus leading to high sludge volume production (about 800 ml 1-1 spent liquor).
Subject: Ciências Tecnológicas, Ciências da engenharia e tecnologias
Technological sciences, Engineering and technology
Scientific areas: Ciências da engenharia e tecnologias
Engineering and technology
Document Type: Artigo em Revista Científica Internacional
Rights: restrictedAccess
Appears in Collections:FEUP - Artigo em Revista Científica Internacional

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