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Neutralization Metal Containing Wastes.

George LC; Ballard LN; Feeler VH
U S Pat 3 736 239 1973 May; :
A cyanide and metals-containing liquid waste is treated by the addition of a second liquid waste containing acids and dissolved metals. Cyanides are quantitatively removed by precipitation with the metals at neutral or slightly alkaline conditions. Thus, a hno3 liquid waste solution from an electroplating operation was used to neutralize an alkaline cyanide-containing waste from another operation. The hno3 waste contained large amounts of dissolved ni and cu, together with small amounts of fe and carbon monoxide Metals in the cyanide waste included ni, cu, and fe. The hno3 waste was added to the cyanide waste until the ph reached approximately 4.5. During the neutralization procedure all evolved gases were collected and scrubbed with 0.1M naoh to recover any hcn produced. After reaction, no cyanide was found in the naoh solution at a detection level of 0.08 Ppm. Nearly all of the original cyanide content was precipitated at ph 9 and cyanide was not detected below a ph of approximately 7.5. Quantitative precipitation of the metals occurred at ph approximately 7-7.5. The precipitated metal cyanides contained cucn, ni(cn)2.4H2o, and cu2fe(cn)6.7H2o. The mixed precipitate analyzed 24.0 pct ni, 23.6 pct cu, and 0.9 pct fe. (Corr: ca 79:45,529b)
Publication Date
Document Type
Fiscal Year
Identifying No.
PAT 3,736,239
NIOSH Division
Source Name
U.S. Pat. 3,736,239; May 29, 1973; Chem. Abstr. 79:139,564M
Page last reviewed: October 1, 2021
Content source: National Institute for Occupational Safety and Health Education and Information Division