Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group va metal or arsenic
Patent
1983-12-05
1985-03-05
Davis, Curtis R.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group va metal or arsenic
423 1, 423 82, 423 92, 423101, 210723, 210724, 210726, C01G 900, C01G 1102, C01G 1900
Patent
active
045030170
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of purifying waste aqueous solutions containing heavy metals, such as zinc, arsenic, cadmium, antimony, lead, mercury and copper, of which at least one of the elements arsenic, antimony, mercury and tin is present in considerable amounts.
Waste solutions containing heavy metals are produced in many different kinds of activities, for example within the mining industry, the chemical-metallurgical industry and the surface-conditioning industry. Rainwater which has drained through heaped waste or has collected within an industrial area may also be contaminated. The term "heavy metals" here and below comprises certain elements such as selenium, arsenic and antimony which strictly speaking are not known as metals in chemical meaning, but which in environmental connection usually are considered as such.
Water which is contaminated with heavy metals is normally purified by adding lime to the water. The lime increases the pH, whereat metal hydroxides are precipitated. Water contaminated with heavy metals may also contain sulphate/sulphite ions originating from an addition of sulphuric acid in some process step or the other, or as a result of the absorption of sulphur dioxide or sulphur trioxide in the water. These sulphur compounds together with lime form gypsum or calcium sulphite. Normally, the lime must also be added in surplus quantities, because it contains an inactive part. Both of these factors mean that the sludge containing heavy metals are obtained when the lime precipitates contains components which do not contain heavy metals and which may often be of the same magnitude with regard to weight as the heavy metal hydroxides. This is a serious disadvantage, both with respect to storage and with respect to working-up said components.
Water containing heavy metals can also be purified by adding sodium hydroxide thereto, so as to form hydroxides. The disadvantages with sodium hydroxide however, is that it is not possible therewith to precipitate such ions as those occurring in solution in the form of negative form, for example arsenic and antimony, and that the metal hydroxide precipitate is difficult to separate from the water.
Proposals have also been made for precipitating heavy metals from mine water contaminated with said metals, with the aid of sulphide, as reported, inter alia, in an article by H. Peter Larsen and Laurence W. Ross (E/MJ-Feb. 1976 p 94-96). In this proposal, sodium hydroxide is added in a first stage to obtain a pH.about.5, whereafter sodium sulphide is added in a given quantity, to precipitate any heavy metals present, such as iron(III), copper, zinc and manganese. Such a sulphide precipitation method as that proposed for mine water, however, has an obvious disadvantage, since its applicability is limited and embraces generally those heavy metals aforementioned in connection with the purification of just mine water. In the case of industrial aqueous waste solutions of the type described in the introduction, it has been found that when applying said sulphide precipitation technique, no purification, or only poor purification, is obtained with respect to particularly high contents of such environmentally important elements as Hg, As, Sb, Sn, Pb, Bi, Cd and Cu. Thus, it has been found when practising the known sulphide precipitation method that if the content of, for example, As(III) and/or Sb(III) is high (>100 mg/l), the hydroxide ions formed with the reaction of these elements with sulphide will increase the pH of the solution to such an extent that the ability of the aforementioned metal ions to react with sulphide is impaired or ceases totally. In this connection, the sulphide-ion content of the solution can readily increase to such an extent that previously precipitated sulphides are brought into solution by complex forming with surplus sulphide ions, for example in accordance with the following schematic reaction: ##STR1## where Me is an element which can form sulphide precipitate in an acid pH but whose sulphide is soluble in sodium sulp
REFERENCES:
patent: 3421850 (1969-11-01), Peterson et al.
patent: 3740331 (1971-06-01), Anderson et al.
Larsen et al., "Two-Stage Process Chemically Treats Mine Drainage to Remove Dissolved Metals," E/MJ-Feb. 1976, pp. 94-96.
Skoog et al., Fundamentals of Analytical Chemistry Holt, Rinehart and Winston, Inc., 1963, pp. 746-748.
Gadd Rolf K.
Sund-Hagelberg Anna C.
Boliden Aktiebolag
Davis Curtis R.
Pak Chung
LandOfFree
Method of purifying waste aqueous solutions from heavy metals does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of purifying waste aqueous solutions from heavy metals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of purifying waste aqueous solutions from heavy metals will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1733890