WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.33 - Sulphates; alums; peroxosulphates (persulphates). - Sodium sulphates : 2833.11 - - Disodium sulphate 2833.19 - - Other - Other sulphates : 2833.21 2833.22 - - Of magnesium - - Of aluminium 2833.24 - - Of nickel 2833.25 - - Of copper 2833.29 - - Other 2833.30 - Alums - Peroxosulphates (persulphates) 2833.40 (A) SULPHATES Subject to the exclusions mentioned in the introduction to this sub-chapter, this heading covers the metal salts of sulphuric acid (&So4) (heading 28.07), but excludes mercury sulphates which fall in heading 28.52, ammonium sulphate which, even pure, falls in headin 31.02 or 31.05 and potasslum sulphate, which, whether or not pure, falls m herding 31.04 or 39.05. (1) Sodium sulphates include : (a) Disodium sulphate (neutral sulphate) (Na2S04).Occurs in the anhydrous or hydrated state as a powder or m large transparent crystals, eMorescin in the air and dissolving in water with a fall in temperature. The decahydrate (Na2 04.10H20) is known as Glauber's salt. Impure forms of disodium sulphate (90 - 99 % purity), obtained as by-products of various manufactunn processes, are often %-~ally escribed as " salt cake ' and are classified in this heading. hsodium sulphate is used as an adjuvant in d eing; as a flux in lass-makulg to obtain vitrifiable mixtures (manufacture o bottle glass, crystal an optical glass); in tanning for preservin hides; in paper-making (preparation of certain chemical pulps); as a sizing materia in the textile industry; in medicine as a purgative, etc. % ?- ?' Y Natural sodium sulphates (glauberite, polyhalite, bloedite, astrakhanite) are excluded (heading 25.30). (b) Sodium hydrogen sulphate (acid sulphate) (NaHSO,). This residual salt of the manufacture of nitric acid occurs in deliquescent fused, white masses. Used instead of sulphuric acid, in particular for picklin metal, regenerating rubber, in the metallurgy of antimony or tantalum and as a weed- ller. &i (c) Disodium disulphate (sodium pyrosulphate) (Na2SzO7). (2) Magnesium sulphate. This headin covers artificial magnesium sulphate $MfS04.1H20) (Epsom salts, Se~dlitzsalts) obtained% uri .ng kieserite, or by the action o su phunc acld on dolomite. Colourless crystals, sligKdy egorescin in air, soluble in water. Used as a filler in sizing textiles, in tanning, for fire-proofing an as a purgative. The heading excludes natural magnesium sulphate (kieserite) (heading 25.30). (3) Aluminium sulphate (d2(S04)3).Obtained by treating bauxite, or natural aluminium silicates, with sulphuric acid; the impuribes are mainly iron corn ounds. In the hydrated state (with 18 H20) it a pears in white crystals, soluble in water, w ich can either be crumbly and easily scratche with a fingernail or hard and brittle, according to the de e of concentration of the solution emplo ed; on gentle heating it melts in its water of crys%sation, giving finally the anhydrous sulp te. Used in dyeing as a mordant; in tanning for serving hdes and for alum tannin ; in paper-making as a size for paper pulp; in the dyesxindushy for making lakes, methy ene blue or other thiazode dyestuffs. Used also for clarifylug tallow, purifying industrial water, in f i e extinguishers, etc. B B E L Basic aluminium sulphate, used in dyeing, is also classified here. (4) Chromium sulphates. The best known is chromic sulphate (&(S04)3), prepared fiom chromium nitrate and sulphuric acid. Crystalline powder, vlolet or een, in aqueous solution. Used as a mordant in dyeing (chrome mordanting) or in tanning (c ome tanning). The main products used for the latter purpose are rather unstable solutions of basic chromium sulphates derived fiom chromic sulphate or fiom chromous sulphate (CrS04). These sulphates are included here. g (5) Nickel sulphates. The most common of these sulphates has the formula NiS04. Anhydrous in yellow crystals, or hydrated in emerald green crystals (with 7 H20) or bluish crystals (with 6 HzO); soluble in water. Used in electrolytic nickel-plating, as a mordant in dyeing, in the preparation of gas masks and as a catalyst. (6) Copper sulphates. (a) Cuprous sulphate (Cu2S04).Catalyst used in the preparation of synthetic ethanol. (b) Cupric sulphate (CuS04.5H20). By-product of obtained by treating copper waste or scrap with a c stals or crystalline powder, soluble in water. It w en calcinated, which absorbs water with avidity. Used as a (see Explanatory Note to heading 38.08); for reparing s raying mixtures; to cuprous oxide or inorganic copper colours; in yeworks ( or-dyemg silk or woo b ack urple or lilac); in electrolytic copper refining or copper-plating; as a flotation regulator ffor restoring the natural buoyancy of ores); as an amseptic, etc. X a P Natural hydrated copper sulphate (brochantite) is excluded (heading 26.03). P"P" (7) Zinc sulphate (ZnS04.7H20). Obtained by the action of dilute sulphuric acid on zinc, zinc oxide, zinc carbonate or roasted blende. White vitreous masses or in needle-shaped crystals. Used for of ores in flotation processes; as a mordant in dyeing; as an antiseptic; for preserving wood; in the manufacture of 32.06), luminophores (zinc sulphate activated by copper) other zinc compounds. (8) Barium sulphate. This heading covers artificial or precipitated barium sulpbate (BaS04) obtained by precipitating a solution of barium chloride with sulphuric acld or an alkali sulphate. Occurs as a white powder, very heavy (specific gravity about 4.4) and insoluble in water, or in a thick paste. Used as a white pigment, as a filler for sizin textiles and in the preparation of rubber, coated paper, paperboard, lutin s, lakes, co ours, etc. It is imperwous to X-rays and is therefore used (pure) in radiograp y. e k Natural barium sulphate (barytes, heavy spar) is excluded (heading 25.11). (9) Iron sulphates. (a) Ferrous sulphate (FeS04). Obtained by treating iron shavings with dilute sulphuric acid or as a b product fiom the manufacture of titanium dioxide; it often contains impurities suc as copper and ferric sulphates and arsenic. Very soluble in water; occurs mainly in the hydrated state ( enerally with 7 H20)in light green crystals and turns brown on exposure to air; t e action of heat transforms them into white anhydrous sulphate. Aqueous solutions are een but turn brownish on exposure to air. Ferrous sulphate is used for preparin inks &on inks), colours (Prussian blue), and the mixture (with slaked lime and saw ust) used for purifjFing coal gas; in dyeing; as a disinfectant, an antiseptic and a herbicide. l- !I (b) Ferric sulphate F ~ ( s 0 4 ) ~Pre ) . ared fiom ferrous sulphate. Powder or as brownish Used slabs. Very solub e in water, w i g which it forms a white hydrate (with 9 H20). for purifying natural waters or sewage, for coa ating blood in slaughterhouses, in iron-tanning and as a fun icide. As it lessens e buoyancy of ores, ~t is used as a flotation regulator. Used a so as a mordant in dyeing and in the electrolytic production of copper or zinc. tP f (10) Cobalt sul hate (CoS04.7H20). Pre ared from cobaltous oxide and sulphuric acid; red crystals so uble in water. Used for e ectrolytic cobalt- lating, as a ceramic colour, as a catalyst and for preparing precipitated cobalt resinates (Aers). P (11) Strontium sul hate. Artificial strontium sulphate (SrS04) precipitated from chloride solution, is a w 'te powder, sparingly soluble in water. Used in pyrotechnics, cexanics and the preparation of various strontium salts. & Native strontium sulphate (celestine) is excluded (heading 25.30). (12) Cadmium sulphate (CdS04 . Colourless crystals, soluble in water, either anhydrous or in the hydrated state (wth 8 I?20). Used in the manufacture of cadmium yellow (cadmium sul lude) or other colouring matters, and of medicinal products; in standard electric cells eston cells); in electroplating and in dyeing. alp (1 3) Lead sulphates. (a) Artificial lead sul hate (PbS04). Obtained fiom lead nitrate or acetate by precipitation with su phuric acid; white powder or crystals, insoluble in water. Used in the manufacture of lead salts. f @) Basic lead sulphate. Prepared as eyish owder by heating together litharge, sodium chloride and sulphuric acld, May a so be o73tained by a metallurgical process, in which case it takes the form of a white powder. Used in the preparation of pigments, mastics and mixtures for the rubber industry. Y Natural lead sulphate (anglesite) is excluded (heading 26.07). (B) ALUMS Alums are hydrated double sulphates containing a sul hate of a trivalent metal (aluminium, chromium, manganese, iron or indium) and a sulphate o a monovalent metal (alkali sulphate or ammonium sulphate). Used in d ein , as anbseptics and in the preparation of chemicals, although there is a tendency to repice %em by simple sulphates. P (1) Aluminium alums. potassium sulphate (ordinary alum or potassium alum) A12(S04)3.K~S04.24Hfl).Obtaned fiom natural alunite (alum stone) (heading 25.30), i.e., basic aluminium-potassium sulphate mixed with aluminium hydroxtde). Alum IS also prepared from the two constituent sulphates. White crystalline solid, soluble in water. On calcination it gives a light white powder, anhydrous and crystalline (calcined alum). Used for the same purposes as aluminium sulphate, in particular in the preparation of lakes, in dyeing and in tanning (alum-tanning). Used also in photography, toilet preparations, etc. @) Aluminium ammonium sulphate (ammonium alum) (A12(S04)3.(NH4)2S04.24H20). Colourless crystals, soluble in water especially when hot. Used in the preparation of pure aluminium oxide and in medicine. b (c) Aluminium sodium sulphate (sodium alum) (Alz S04)3.Na2S04.24H20).Similar to potassium alum, occurs in efflorescent crystals, solu le in water. Used as a mordant in dyeing. (2) Chromium alums. (a) Chromium potassium sulphate (chrome alum) (Cr2(S04)3.K2S04.24Hz0). Obtained by reducing a solution of otassium &chromate in sulphuric acid with sul hur dioxide. Forms purplish-red crysta s, soluble in water and efflorescing in the air. sed in dyeing as a mordant, in tanning (chrome-tanning), in photography, etc. P up (b) Ammonium chromium sulphate (chrome ammonium alum). Crystalline blue powder, used in tanning and in ceramcs. (3) Iron alums. Ammonium iron bis (sulphate) ((NH4)2S04.Fe2(S04)3.24H~O),in purple crystals dehydratin and turning white in the air; iron (III) potassium sulphate also in purple crystals. Bot are used in dyeing. K (C) PEROXOSULPHATES (PERSULPHATES) The name peroxosulphates (persul hates) is reserved for the salts of the peroxosulphuric (persulphunc) acids of heading 28. 1. They are fairly stable in the dry state but in aqueous solution they are decomposed on heating. Powerful oxidising agents. (2) Disodium peroxodisul hate (Na2S20S).Colourless c stals, very soluble in water. Used as a disinfectant, in bleac ing, as a depolarising agent Tatteries) and for engraving copper alloys. % (3) Dipotassium qeroxodisulphate (K2SzOs).Colourless crystals, very soluble in water. Used for bleaching, in soap-malung, in photography, as an antiseptic, etc. Natural calcium sulphates (gypsum, anhydrite, karstenite) are excluded (heading 25.20).
1.- Except where the context otherwise requires, the headings of this Chapter apply only to : (a) Separate chemical elements and separate chemically defined compounds, whether or not containing impurities; (b) The products mentioned in (a) above dissolved in water; (c) The products mentioned in (a) above dissolved in other solvents provided that the solution constitutes a normal and necessary method of putting up these products adopted solely for reasons of safety or for transport and that the solvent does not render the product particularly suitable for specific use rather than for general use; (d) The products mentioned in (a), (b) or (c) above with an added stabiliser (including an anti-caking agent) necessary for their preservation or transport; (e) The products mentioned in (a), (b), (c) or (d) above with an added anti-dusting agent or a colouring substance added to facilitate their identification or for safety reasons, provided that the additions do not render the product particularly suitable for specific use rather than for general use.