GB818379A - Treatment of manganese solutions - Google Patents

Abstract

Manganese - bearing solutions and particularly those forming a waste product in uranium recovery processes, containing iron and a metal or metals of the group cobalt and nickel are purified by bringing the pH of the solution to between 4 and 6 to precipitate ferric iron which is separated and thereafter bringing the solution to a pH over 8 to precipitate manganese together with nickel and cobalt, separating such precipitate and dissolving it in a suitable solvent, preferably sulphuric acid to form a second solution from which the nickel and cobalt are precipitated and thereafter treating the resulting solution for the recover of the manganese values therein. The iron in the original solution normally is in the ferrous state and is first oxidized to ferric iron with sodium or potassium permanganate or dichromate but preferably with a manganese compound in the manganic state, suitably an ore containing manganese dioxide, or manganese hydrates which have been allowed to oxidize. The process is illustrated in the flow sheet (Fig. 1) wherein, in the first step the ferrous iron is oxidized to ferric iron and in the second step the pH is adjusted preferably between 5 and 6 to precipitate ferric iron as hydrate. Suitable neutralizers are lime or lime-stone, but preferably reduced manganese ores are employed. Arsenic and cadmium, if present are precipitated with the ferric iron. If desired, the first and second steps may be combined as one step, in which case the solution is treated with a manganese ore which has been partially roasted or with a hydrate that contains sufficient manganese to convert the ferrous iron to ferric and to neutralize the solution. After separation of the iron precipitate the solution is treated in step 3 with an alkali such as lime at a pH above 8 to precipitate, as hydroxides, manganese together with nickel and cobalt. A pH of 9.5 is preferred. These metals precipitate as hydroxides and oxygen should be excluded from the reaction and a reducing agent such as sulphur dioxide or sodium sulphite may be added to the solution to counteract the effect of atmospheric oxygen. The hydroxide concentrate is then treated in step 4 with sulphuric acid (which may be the anolyte from an electrolytic plant) if desired in the presence of a reducing agent such as sulphur dioxide but preferably ferrous <PICT:0818379/III/1> <PICT:0818379/III/2> iron formed by addition of scrap iron. The calcium sulphate formed is separated by filtration. The solution passes to step 5 where it is treated with ammonium sulphide or other soluble sulphide at a pH of about 6.5 thereby precipitating nickel and cobalt sulphides. The precipitation may be accelerated by the use of finely divided materials such as "Celite" (Registered Trade Mark), activated charcoal or alumina or mica. The manganese containing solution may then be passed to a step 7 for the electrolytic recovery of metallic manganese or manganese oxide, or the manganese may be recovered as manganese sulphate; alternatively the solution may be passed to step 8 where it is treated with lime in the presence of oxygen at elevated temperature to precipitate a complex mixture of a calcium and manganese oxides in which some of the manganese is present as dioxide. Alternatively sufficient lime may be added to the solution from step 5 to precipitate manganese hydrate which may be allowed to oxidize to manganic hydroxide for use in step 1 of the process. An alternative process is shown in Fig. 2, wherein steps 1 to 5 are carried out as before. From step 5 the solution passes to step 6 where it is treated with ammonium hydroxide to precipitate manganese hydrate optionally in the presence of a reducing agent such as sulphurous acid or hydroxylamine sulphate; alternatively, ammonium carbonate may be used as a precipitant, as shown, where carbon dioxide is bubbled into the solution and ammonium hydroxide is added. The manganese carbonate precipitate may be dissolved in an electrolytic anolyte as shown in step 7 and the carbon dioxide evolved is passed to step 6. Specification 818,380 is referred to.