| 摘要 |
In a process for removing contaminants wherein a coagulating agent is used there is also used as a coagulant aid a cellulose derivative which is either water-soluble or alternatively alkali-soluble and water-insoluble. The preferred concentration is 0.5 to 5 parts by weight per million parts by weight of water, in the range 0.1 to 10. Examples of cellulose derivatives are: a sodium salt of carboxymethyl cellulose; a sodium salt of a sulphaethyl cellulose; a methyl cellulose; an oxidized cellulose; a salt of cellulose sulphate; a hydroxyethyl-cellulose which contains from 0.1 to .8, preferably from 0.25 to 0.5 hydroxyethyl substituent per anhydroglucose unit and is alkali-soluble and water-insoluble; a hydroxyethyl cellulose which contains more than 0.8 but not more than 2 hydroxyethyl substituents per anhydroglucose unit and is water-soluble. The coagulating agent may be aluminium sulphate, ferric sulphate, ferric chloride or sodium aluminate. The cellulose derivative may be added to the contaminated liquid in the form of a powder but where it is water-soluble it is preferably added in the form of an aqueous solution, and where it is alkali-soluble and water-insoluble it is preferably added in the form of a suspension prepared by dissolving the derivative in a caustic alkali solution and diluting with water. The cellulsoe derivative may be added to the contaminated water prior to the introduction of coagulating agent, with the agent, or, preferably after a flux has been formed by addition of such agent. Comparative examples are given in the Specification. In most instances the solubility characteristics of a cellulose derivative are determined by the number of substituents per anhydroglucose unit, but may vary, and depend upon uniformity of substitution, method of preparation and the like. For example, sodium carboxymethylcellulose having a degree of substitution below 0.35 is water-insoluble, at 0.35 is partially water-in-soluble and at 0.4 to 0.5 becomes completely water-soluble. An acidic or basic compound may be added in the process for pH adjustment. The mixture of contaminated liquid and reagent is agitated for from 30 to 60 minutes (though in some instances 10 minutes is sufficient), preferably in a sludge blanket apparatus. The cellulose derivatives can be used singly or in combination with any of the others. They may also be used with other coagulant aids such as poly-vinyl acetate.
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