Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1993-03-18
1995-09-19
McCarthy, Neil
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
210721, 210724, 210906, 210908, 210912, 210915, 252175, 423511, 423562, 423565, C02F 162
Patent
active
054513278
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a composition for treating water containing metal ions and organic and/or inorganic impurities, and further relates to a method of manufacturing said composition, and to the use of said composition for removing toxic and nonferrous heavy metals and dissolved, suspended, or emulsified organic and/or inorganic components from aqueous systems.
BACKGROUND OF THE INVENTION
Toxic heavy metals and nonferrous heavy metals are widely used in all industrial countries as components of alloys in steels and as finishing or corrosion-resistant coating materials in combination with plastics and natural products. In modern manufacturing technologies, metals from the A groups and some of the heavy metals from groups III-B, IV-B, and V-B of the periodic table provide advantages but also present environmental discharge problems.
By conservative estimates, about 5% of the metal elements produced or used in manufacturing or treatment processes are left behind as residues or wastes, in pure form or in compounds, which residues and wastes cannot be economically reused by presently known methods. In addition to the economic considerations, whereby it would be desirable to be able to economically recover the valuable materials and thus reduce the costs and foreign exchange requirements for purchasing the raw materials, from an environmental standpoint it is also important to be able to reduce the disposal burden of toxic and nonferrous heavy metals, which metals are toxic to nearly all biological species.
The removal of toxic and nonferrous heavy metals from waste waters of the metal processing industry is currently accomplished primarily by classical hydroxide precipitation with sodium hydroxide, milk of lime, or, in special cases, sodium carbonate. Because of the wide pH range in which the hydroxides and oxyhydrates precipitate, and because of mixed reactions, i.e., reactions of disparate divalent metal ions with different ion radii, for each metal ion mixture it is necessary to carry out preliminary tests to determine empirically the optimal "compromise" pH value. Further, it is not possible to make exactly reproducible predictions concerning the precipitation process, because numerous factors affect and can interfere with the precipitation process. Hydroxide precipitation of toxic and nonferrous heavy metals has basically four additional inherent disadvantages: -10.sup.10 greater than those of the corresponding sulfides. The solubilities of the metal hydroxides thus are cumulative, depending on the matrix conditions of the solutions, up to values tens of millions of times higher than those of the corresponding sulfides. increased solubility, is much stronger for hydroxide precipitation than for sulfide precipitation. Also, frequently neutral salts have deleterious effects on the sedimentation characteristics and the filterability of the precipitates. is impossible or inadequate in the presence of complex-forming agents. except by the use of difficult and costly methods. Therefore, as a rule, heretofore, hydroxide sludges from the metal processing industry have been disposed of at high cost as special toxic wastes.
In contrast, the solubility products of most metal sulfides are so low that the metals can be precipitated quantitatively even from solutions containing strong complexes. Nonetheless, sulfide precipitation is rare in waste water treatment practice. One reason for this is the problems associated with the use of hydrogen sulfide, which is unpleasant smelling, toxic, and flammable; another reason is that most metal sulfides are difficult to remove to a satisfactory degree from the water phase.
In recent years, various organosulfides have been used in waste water purification practice. The organosulfides operate on the same principle as the sulfides, and precipitate, as sulfides, metals such as (among others) copper, cadmium, mercury, lead, nickel, tin, and zinc. However, organosulfides have the disadvantage that the allowable pH values are in the range >7, b
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Chemical Abstracts 97: 147038e.
Immobilisation, Entgiftung . . . Martinez, p. 147.
Angeli Michael de
McCarthy Neil
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