Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1988-06-06
1989-11-28
Cintins, Ivars
Liquid purification or separation
Processes
Ion exchange or selective sorption
210684, 210688, C02F 142
Patent
active
048835994
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for cleansing metal-containing solutions that are rich in salt, and apparatus herefor.
It is known that certain metals, primarily mercury, cadmium and lead, have a serious negative effect on different ecological systems. Consequently, it is necessary to find ways and means of extracting such deleterious substances from, inter alia, different types of flue gases and process water.
Swedish patent specification No. 440 608the corresponding U.S. Pat. No. 4,583,999 dated Apr. 22, 1986, Swedish patent application 860 2495-7 and Swedish patent application No. 860 2989-9 teach gas-cleansing methods in which, inter alia, mercury is extracted. According to these methods mercury, among other substances, is captured in an acid condensate, the mercury forming a chloride complex. Cadmium is also a substance which is extracted from flue gas in this way.
Mercury has a great tendency towards forming complexes in water with both organic and inorganic ligands. In order to extract mercury from a complex aqueous solution, it is necessary to add an agent with which the mercury present will form a still more stable compound. Inorganic and organic sulphides, such as TMT 15 or Na.sub.2 S, can both be used for this purpose. The resultant mercury sulphide precipitate, however, has an extremely fine granular form and is consequently difficult to separate.
The extent to which the metal sulphides can be extracted in practice is contingent on the efficiency of those parts of the cleansing process in which the metal precipitates are separated from the system. The results obtained hitherto from such systems indicate that the residual contents are normally so high as to require access to large water recipients in order not to create ecological effects.
The above applies both to water that has become contaminated when used in gas cleansing processes, and other industrial process water.
Consequently, one problem is to achieve a sufficiently high degree of separation or extraction of the mercury-containing metal precipitates.
Another problem resides in the very large volumes of water used in known cleansing systems. Consequently, it is desirable to be able to concentrate the mercury compounds so that they are present in a smaller volume of water prior to their final extraction from the system.
The same applies to other metals, such as cadmium and lead.
These problems are solved by the present invention, which provides a simple method and simple apparatus for extracting mutually different metals, primarily mercury, cadmium and lead.
Accordingly, the present invention relates to a method for cleansing metal-containing solutions, particularly process water that contains metals such as mercury, cadmium and/or lead, where the metal concerned is in a water-solution form, such as the form of a chloride complex, the method being characterized by passing the solution through an ion-exchange material which consists essentially of sulfhydrated cellulose, said metals being adsorbed in the sulfhydrated cellulose; by regenerating said ion-exchange material subsequent to having adsorbed a given quantity of metal, wherein an aqueous solution containing hydrochloric acid (HCL) having a concentration of at least about 1 molar HCL is flushed or rinsed through said ion-exchange material; and by causing, in a known manner, the metal concerned to precipitate in a sulphide form from the liquid eluted from the ion-exchange material when rinsing said material.
The invention also relates to apparatus of the kind by which the aforementioned method may be practised, namely apparatus for cleansing metal-containing solutions, particularly, but not exclusively, process water which contains such metals as mercury, cadmium and/or lead, where the metals concerned are present in a water-soluble form, such as in a chloride complex form, and wherein the apparatus includes an ion-exchange column which is provided with an inlet pipe for contaminated liquid and an outlet pipe for cleansed liquid, and which contains an ion-exchange material
REFERENCES:
patent: 3755161 (1973-08-01), Yokota et al.
patent: 4752398 (1988-06-01), Holbein et al.
Hovsenius Gunnar
Lindahl Erik
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