Chromium precipitation from tanning spent liquors with industrial alkaline residues: a comparative study

• Type: Article in International Scientific Journal
• Date: 1997

Authors

M. A. Fonseca Almeida (Author) FEUP; Rui A. R. Boaventura (Author) FEUP

Journal

Title: Waste Management

Vol. 17 No. 4

Pages: 201-209

ISSN: 0956-053X

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 18 Citations

ISI Web of Science

Scopus - 26 Citations

COMPENDEX

Other information

Authenticus ID: P-001-D1E

DOI: 10.1016/S0956-053X(97)10006-X

Abstract (EN): 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 g l(-1) residual Cr remains greater than or equal to 3.7 mg l(-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 g l(-1) (dry basis) of chemical sludge from a water treatment plant results in a removal efficiency of 99.97% Cr and residual Cr less than or equal to 2 mg l(-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 l(-1). However, during Cr precipitation, Al is leached from the added product up to about 40 mg Al per litre of supernatant; (iii) precipitation using acetylene production sludge only requires a dosage of 16 g l(-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 less than or equal to 2 mg l(-1) and the sludge volume about 500 ml l(-1). This Cr level can also be achieved at a dosage of 14 g l(-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 g l(-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 l(-1). Additionally, the resulting sludge is not very dense, thus leading to high sludge volume production (about 800 ml l(-1) spent liquor).

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 9