Abstract:
A method for treating a waste material (20) containing sulfuric acid and metal ions, as In the case of the waste material the production of the T1O2, provides mixing to the waste material (20) an alkaline reagent (10), selected among a hydroxide of an alkaline metal such as Mg, Zn, Sn, adapted to selectively precipitate (300) the cations as hydroxides, thus obtaining a first mixture (21) having a higher pH that contains a solution (22) of a sulfate and/or oxysulfate of the metal and solid hydroxides (23) of the metal cations that are separated from the first mixture (21) and can be used in metal sulfates production process. The method also comprises mixing the solution (22) with a precipitation agent (31), thus forming a second mixture (32) in which the sulfate and/or oxysulfate precipitates and is removed (301), heated, reduced and decomposed (400) by means of a reducing agent (41) selected among elemental sulfur, hydrogen and a reducing flame, thus obtaining SO 2 (42) available for making H 2 SO 4 , and a solid oxide (43) of the metal of the alkaline reagent that is recycled (101) as alkaline reagent (10) in the step (200) of mixing with the waste material (20). Advantageously, a step (350) is provided of recovering precipitation agent (31) from the water of second mixture (32), after removing (301) the sulfate and/or oxysulfate, and a step (351) is also provided of recycling the regenerated precipitation agent (31), In particular, an alcohol as ethyl alcohol, used as the precipitation agent (31), can be easily regenerated by distillation, exploiting low temperature-heat, which is largely available from a possible sulfuric acid production plant close to the plant that producing the sulfuric waste material (20). The method according to the invention makes it possible to eliminate the sludge resulting from the sulfuric waste material treatment, while recovering valuable compounds.
Abstract:
A method (10) for the recovery of solid magnesium sulphate from a process solution (12) containing dissolved magnesium sulphate. The method comprises concentrating the process solution (12) using membrane filtration (16) to form a concentrated process solution, and treating the concentrated process solution to precipitate solid magnesium sulphate.
Abstract:
The invention provides a process for producing magnesium oxide from fly ash or slag comprising magnesium and iron, the process comprising: leaching the fly ash or slag with an aqueous mineral acid solution to produce a leaching solution and a residue, the leaching solution comprising a magnesium salt and an iron salt; precipitating the iron salt by increasing the pH of the leaching solution to above 3.5, and separating the leaching solution from the precipitated iron salt; and forming magnesium oxide by decomposing the magnesium salt present in the leaching solution.
Abstract:
A method (10) for the recovery of solid magnesium sulphate from a process solution (12) containing dissolved magnesium sulphate. The method comprises concentrating the process solution (12) using membrane filtration (16) to form a concentrated process solution, and treating the concentrated process solution to precipitate solid magnesium sulphate.