A method for efficiently removal of oxidised selenium from liquid, such as FGD wastewater. The method involves adding a non-iron-based reducing agent (e.g. sodium dithionite) and preferably Fe(II) ions to the liquid at a pH of above 7.5 or 8 and precipitating elemental selenium from the liquid.

A method for efficiently removal of oxidised selenium from liquid, such as FGD wastewater. The method involves adding a non-iron-based reducing agent (e.g. sodium dithionite) and preferably Fe(II) ions to the liquid at a pH of above 7.5 or 8 and precipitating elemental selenium from the liquid.

A method for efficiently removal of oxidised selenium from liquid, such as FGD wastewater. The method involves adding a non-iron-based reducing agent (e.g. sodium dithionite) and preferably Fe(II) ions to the liquid at a pH of above 7.5 or 8 and precipitating elemental selenium from the liquid.

A process and a system allow producing sodium hydrosulfite crystals. A suspension containing sodium hydrosulfite is provided. The sodium hydrosulfite crystals are separated from a remainder of the suspension. The separated sodium hydrosulfite crystals are cooled to a stable temperature. The suspension may be obtained by raising a pH and lowering a temperature of a solution containing sodium hydrosulfite. A partial precipitation of the sodium hydrosulfite to form the crystals may be facilitated by addition of a nucleating agent to the suspension.

A process and a system allow producing sodium hydrosulfite crystals. A suspension containing sodium hydrosulfite is provided. The sodium hydrosulfite crystals are separated from a remainder of the suspension. The separated sodium hydrosulfite crystals are cooled to a stable temperature. The suspension may be obtained by raising a pH and lowering a temperature of a solution containing sodium hydrosulfite. A partial precipitation of the sodium hydrosulfite to form the crystals may be facilitated by addition of a nucleating agent to the suspension.

A process and a system allow producing sodium hydrosulfite crystals. A suspension containing sodium hydrosulfite is provided. The sodium hydrosulfite crystals are separated from a remainder of the suspension. The separated sodium hydrosulfite crystals are cooled to a stable temperature. The suspension may be obtained by raising a pH and lowering a temperature of a solution containing sodium hydrosulfite. A partial precipitation of the sodium hydrosulfite to form the crystals may be facilitated by addition of a nucleating agent to the suspension.

A process and a system allow producing sodium hydrosulfite crystals. A suspension containing sodium hydrosulfite is provided. The sodium hydrosulfite crystals are separated from a remainder of the suspension. The separated sodium hydrosulfite crystals are cooled to a stable temperature. The suspension may be obtained by raising a pH and lowering a temperature of a solution containing sodium hydrosulfite. A partial precipitation of the sodium hydrosulfite to form the crystals may be facilitated by addition of a nucleating agent to the suspension.

A process for the production of hydrosulphite is described, which provides the mixing of said hydrosulphite with one or more acids chosen among 4-aminobenzoic acid, 4-hydroxybenzoic acid or 4-methylbenzoic acid and with an alkaline salt of oxalic acid. Optionally, a compound is added, chosen among one or more alkaline carbonates and one or more alkaline tripolyphosphates. Advantageously, the components added to hydrosulphite make up a percentage ranging between 0.1 and 20% by weight of the total hydrosulphite. A formulation is also described, containing sodium hydrosulphite and between 0.1 and 20% by weight of a mixture containing: one or more acids chosen among 4-aminobenzoic acid, 4-hydroxybenzoic acid or 4-methylbenzoic acid; an alkaline salt of oxalic acid and possibly one or more alkaline carbonates; one or more alkaline tripolyphosphates.

The present invention relates to a method for reducing or preventing the decomposition of a composition Z comprising Z1 a salt of dithionous acid in an amount ranging from 50 to 100 wt % and optionally Z2 an additive selected from the group consisting of alkali metal carbonate, alkaline earth metal carbonate, alkali metal or alkaline earth metal tripolyphosphate (Na.sub.5P.sub.3O.sub.10), alkali metal or alkaline earth metal sulfite, disulfite or sulfate, dextrose and complexing agents in a combined amount ranging from 0.0001 to 40 wt %, which comprises contacting the components Z1 and optionally Z2 in the solid and/or dry or solvent-dissolved or -suspended state with at least one of the following compounds V in the solid and/or dry or solvent-dissolved or -suspended state, wherein the compounds V are selected from the group consisting of: (a) oxides of the alkali metals lithium, sodium, potassium, rubidium, cesium, or of magnesium, (b) sodium tetrahydroborate (NaBH.sub.4), (c) anhydrous copper(II) sulfate (Cu(SO.sub.4)), phosphorus pentoxide and (d) basic amino acids arginine, lysine, histidine, wherein the solvent for Z1, optionally Z2 and V is practically water-free.

A process for producing alumina, the process having a seeding phase and a precipitation phase. During the seeding phase a seed mixture is produced by adding an aluminium salt to an aqueous solution and then adding an alkaline metal aluminate to the mixture while maintaining the seed mixture at generally neutral pH. The precipitation phase produces precipitated alumina by simultaneously adding aluminium salt and alkaline metal aluminate to the seed mixture while maintaining a pH from 6.9 to 7.8. The recovered precipitated alumina has at least one, preferably all the following characteristics: i) a crystallite size of 33-42 Ang.: in the (120) diagonal plane (using XRD); ii) a crystallite d-spacing (020) of between 6.30-6.59 Ang.; iii) a high porosity with an average pore diameter of 115-166 Ang.; iv) a relatively low bulk density of 250-350 kg/m.sup.3; v) a surface area after calcination for 24 hours at 1100 C. of 60-80 m.sup.2/g; and vi) a pore volume after calcination for one hour at 1000 C. 0.8-1.1 m.sup.3/g.