WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.36 - Carbonates; peroxocarbonates (percarbonates); commercial ammonium carbonate containing ammonium carbarnate. 2836.20 2836.30 - Disodium carbonate - Sodium hydrogencarbonate (sodium bicarbonate) 2836.40 - Potassium carbonates 2836.50 2836.60 - Calcium carbonate - Barium carbonate - Other : 2836.9 1 2836.92 2836.99 - - Lithium carbonates - - Strontium carbonate - - Other Subject to the exclusions mentioned in the introduction to this sub-chapter, this heading covers : (I) Carbonates (neutral carbonates, hydro encarbonates or bicarbonates, basic carbonates) - metal salts of the non-isolate carbonic acid (H2C03), whose anhydride (C02)falls m heading 28.11. B (11) Peroxocarbonates (percarbonates), i.e., carbonates containing an excess of oxygen, such as (Na2C04)(peroxomonocarbonates or (Na2C206)(peroxodicarbonates); these result fiom the action of carbon dioxide on metaI)peroxides. (A) CARBONATES (1) Ammonium carbonates. Obtained by heating a mixture of chalk and ammonium sulphate (or chloride), or by combining carbon dioxide with gaseous ammonia in presence of steam. These processes ve commercial ammonium carbonate which, in addition to various im urihes (chlori es, sulphates, organic matter), contains ammonium hydrogen carbonate an ammonium carbarnate (NH2COOW). Commercial ammonium carbonate (included in this heading) occurs in white crystalline masses or in powder, soluble in hot water. It deteriorates m a humid atmosphere with superficial formation of the acid carbonate, but may still be used in this state. tl f- Ammonium carbonate is used as a mordant in textile dyeing or printing; as a detergent for wool; an expectorant in medicine; in the manufacture of smelling salts or of baking powders; in tanning; in the rubber industry; in cadrmum metallurgy; in organic synthesis, etc. (2) Sodium carbonates. (a) Disodium carbonate (neutral carbonate) (Na2C03). Im roperly called " carbonate of soda " or " commercial soda "; not to be confused wit sodium h droxide (caustic soda) of beading 28.15. May be obtained by heating a solution of sozum chlor~deand ammonia with carbon dioxide, and decomposing by heating the resulting acid sodium carbonate. R Occurs as an anhydrous (or dehydrated) powder, or in hydrated crystals (soda crystals, washing soda) with 10 H20, efflorescing in the air to give a monohydrate (with 1 H20 . Used in numerous industries : as a flux in glass-malung and in ceramics; in the texti e 1' (b) Sodium hydro encarbonate (acid carbonate, sodium bicarbonate) (NaHC03). Usual1 a crysta ine powder or white crystals, soluble in water, es ecially when hot, and lia le to deteriorate in a humid atmosphere. Used in medicine ( or t r e a t i n g r l ) ; for manufacturing digestive tablets and aerated beverages; in the preparation o baking powders; in the porcelain industry, etc. i i ? Natural sodium carbonate (natron, etc.) is excluded (heading 25.30). (3) Potassium carbonates. (a) Di otassium erly called" otash "; not heading 28. 5. Obtained to e confused with from vegetable ffom potassium chloride. White, crystalline masses, very deliquescent, soluble in water. Used in the manufacture of glass or ceramics; for bleaching linen or scouring textiles; to clean paintings; to prepare potassium salts, cyanides, Prussian blue; as an anti-scale preparation, etc. I' \ (b) Potassium hydrogencarbonate (acid carbonate, potassium bicarbonate) (KHCO,). Prepared by the action of carbon dioxide on the neutral carbonate; white crystals, soluble in water, slight1 deliquescent. Used in fre-extinguishers; in the preparation of baking powders; in me 'cine and in oenology (anti-acid). (4) Precipitated calcium carbonate. Precipitated calcium carbonate (CaC03) included in this heading results fiom the treatment of solutions of calcium salts with carbon dioxide. Used as an extender, in the preparation of toothpastes and face-powder, in medicine (treatment of rickets), etc. The heading excludes natural limestone (Cha ter 25) and chalk (naturaI calcium carbonate), whether or not washed and ground (heading 2g09 and calcium carbonate in powder fnm, the particles of which are coated with a water-repellent lm of fatty acids (e.g., steanc acid) (heading 38.24). h (5) Precipitated barium carbonate. Precipitated barium carbonate (BaC03) included in this heading is obtained fiom sodium carbonate and barium sulphide. White powder insoluble in water. Used for purifying industrial water; for manufacturing arasiticides, optical glass and pure barium oxide; as a pigment and flux in enamels; in &e rubber, paper, soap or sugar industries; in pyrotechnics (green lights). Natural barium carbonate (witherite) is excluded (heading 25.11). (6) Lead carbonates. Artificial lead carbonates, included in this heading, are : (a) Neutral lead carbonate @bC03).White powder, crystalline or amorphous, insoluble in water. Used in ceramics and in the manufacture of pigments, mastics and indigo. (b) Basic lead carbonates of the are known as " white lead ". e 2 PbC03.Pb(OH2)in powder, cakes, scales or paste, 8% te lead is obtained from lead acetate resulting from the action of acetic acid on sheet lead or litharge; a drylng pigment. Used in the manufacture of oil aints, of fluxes, of special mastics (e.g., for steam-pipe joints) and of orange lead. ~ & t lead e (used alone or mixed with barium sulphate, zinc oxide, gypsum or kaolin) gives &ems white, Venetian white, Hamburg white, etc. Natural lead carbonate (cerussite) is excluded (heading 26.07). (7) Lithium carbonates. Neutral lithium carbonate (Li2C03),obtained by precipitatin lithium sulphate with sodium carbonate; white crystalline powder, odourless, unaffecte by air, sparingly soluble in water. Used in medicine (uric diathesis) and in the preparation of mixtures for artificial mineral waters. (8) Precipitated strontium carbonate. Precipitated strontium carbonate (SrC03) included in this heading is a very fine white powder, insoluble in water. Used in pyrotechnics (red lights) and in the preparation of iridescent glass, luminous paints, strontium oxide or strontium salts. Natural strontium carbonate (strontianite) is excluded (heading 25.30). (9) Bismuth carbonate. Artificial bismuth carbonate included in this heading is essentially basic bismuth carbonate (bismuthyl carbonate) ( BiO ~COJ),white or ellowish amorphous powder, insoluble in water. Used m medicine an in e manufacture o cosmetics. $ F Natural bismuth hydrocarbonate (bismutite) is excluded (heading 26.17). (10) Precipitated magnesium carbonate. Preci itated magnesium carbonate, included in this heading, is a basic, hydrated carbonate. Bbtained by double decomposition of sodium carbonate and magnesium sul hate. Odourless white product, practically insoluble in water. Light carbonate is the p armacists' white magnesia, a laxative often presented in cubes. Heavy carbonate is a granular white powder. Magnesium carbonate IS used as a filler for paper or rubber; also used in cosmetics and as a heat-insulating material. \ The heading excludes naturaI magnesium carbonate (magnesite) (heading 25.19). (11) Man anese carbonates. Artificial carbonate inclu ed in this heading, is a fine powder, Used as a pigment in paints, rubber and Pr Natural manganese carbonate (rhodocrosite or dialogite) is excluded (heading 26.02). (12) Iron carbonates. Artificial carbonate (FeC03) anhydrous or hydrated (with 1 HzO) included in this heading, is obtained by double decom osition of iron sulphate and sodium carbonate. Greyish crystals, insoluble in water, read y oxidised by air, especially when damp. Used in the preparation of iron salts and of medicaments. ? Natural iron carbonate (siderite or chalybite) is excluded (heading 26.01). 2,. r (13) Cobalt carbonates. Cobalt carbonate (CoC03 anh drous or hydrated (with 6 H20) is a crystalline owder, pink, red or greenish, an inso uble in water. Used as a pigment in enamels an for preparing cobalt oxides or salts. i (14) Nickel carbonates. Normal artificial nickel carbonate (NiCO?) is a light een owder, insoluble in water; used as a pigment in ceramics and in the preparation o nicke oxide. F. 7 Hydrated basic carbonate, in greenish crystals, is used ~n ceramics, glass-making, electroplating, etc. Natural basic nickel carbonate (zaratite) is excluded (heading 25.30). (15) Copper carbonates. Artificial carbonates, also called artificial malachite or artificial azure copper, are eenish-blue owders, poisonous and insoluble in water, consisting of neutral carbonate ( uC03) or o basic carbonates of various kinds. Pre z e d from sodium carbonate and copper sulphate. Used as pigments, pure or mixed (b ue or green copper carbonate, mountain blue or green); as insecticides or fungicides; in medicine (astringents and antidotes against phosphorus poisoning); in electroplating; in pyrotechnics, etc. !f !! P Natural copper carbonate, hydrated or not (malachite, azurite) is excluded (heading 26.03). (16) Precipitated zinc carbonate. Precipitated zinc carbonate (ZnC03) included in this heading is obtained by double decornpos~tionof sodium carbonate and zinc sulphate; white crystalline powder, practically insoluble in water. Used as a pigment in paints, rubber, ceramics and cosmetics. Natural zinc carbonate (smithsonite) is excluded (heading 26.08). (B) PEROXOCARBONATES (PERCARBONATES) (1) Sodium peroxocarbonates. Prepared by treating sodium peroxide, hydrated or not, with liquid carbon dioxide. White owders, dissoIving in water to form oxygen and neutral sodium carbonate. Used for b eaching, in the preparabon of domestic detergents and in photography. P (2) Potassium peroxocarbonates. Obtained by electrolysing at -10 O C or -15 OC a saturated solution of neutral potassium carbonate. White crystals, very hygroscopic, turning blue in a humid atmosphere and soluble in water. Strong oxidising agents sometimes used for bleaching. (3) Other peroxocarbonates, e.g., ammonium or barium peroxocarbonates.
Notes. 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. 2.- In addition to dithionites and sulphoxylates, stabilised with organic substances (heading 28.31), carbonates and peroxocarbonates of inorganic bases (heading 28.36), cyanides, cyanide oxides and complex cyanides of inorganic bases (heading 28.37), fulminates, cyanates and thiocyanates, of inorganic bases (heading 28.42), organic products included in heading 28.43 to 28.46 and 28.52 and carbides (heading 28.49), only the following compounds of carbon are to be classified in this Chapter : (a) Oxides of carbon, hydrogen cyanide and fulminic, isocyanic, thiocyanic and other simple or complex cyanogen acids (heading 28.11); (b) Halide oxides of carbon (heading 28.12); (c) Carbon disulphide (heading 28.13); (d) Thiocarbonates, selenocarbonates, tellurocarbonates, selenocyanates, tellurocyanates, tetrathiocyanatodiamminochromates (reineckates) and other complex cyanates, of inorganic bases (heading 28.42); (e) Hydrogen peroxide, solidified with urea (heading 28.47), carbon oxysulphide, thiocarbonyl halides, cyanogen, cyanogen halides and cyanamide and its metal derivatives (heading 28.53) other than calcium cyanamide, whether or not pure (Chapter 31). 3.- Subject to the provisions of Note 1 to Section VI, this Chapter does not cover : (a) Sodium chloride or magnesium oxide, whether or not pure, or other products of Section V; (b) Organo-inorganic compounds other than those mentioned in Note 2 above; (c) Products mentioned in Note 2, 3, 4 or 5 to Chapter 31; (d) Inorganic products of a kind used as luminophores, of heading 32.06; glass frit and other glass in the form of powder, granules or flakes, of heading 32.07; (e) Artificial graphite (heading 38.01); products put up as charges for fire-extinguishers or put up in fire- extinguishing grenades, of heading 38.13; ink removers put up in packings for retail sale, of heading 38.24; cultured crystals (other than optical elements) weighing not less than 2.5 g each, of the halides of the alkali or alkaline-earth metals, of heading 38.24; (f) Precious or semi-precious stones (natural, synthetic or reconstructed) or dust or powder of such stones (headings 71.02 to 71.05), or precious metals or precious metal alloys of Chapter 71; (g) The metals, whether or not pure, metal alloys or cermets, including sintered metal carbides (metal carbides sintered with a metal), of Section XV; or (h) Optical elements, for example, of the halides of the alkali or alkaline-earth metals (heading 90.01). 4.- Chemically defined complex acids consisting of a non-metal acid of sub-Chapter II and a metal acid of sub-Chapter IV are to be classified in heading 28.11. 5.- Headings 28.26 to 28.42 apply only to metal or ammonium salts or peroxysalts. Except where the context otherwise requires, double or complex salts are to be classified in heading 28.42. 6.- Heading 28.44 applies only to : (a) Technetium (atomic No. 43), promethium (atomic No. 61), polonium (atomic No. 84) and all elements with an atomic number greater than 84; (b) Natural or artificial radioactive isotopes (including those of the precious metals or of the base metals of Sections XIV and XV), whether or not mixed together; (c) Compounds, inorganic or organic, of these elements or isotopes, whether or not chemically defined, whether or not mixed together; (d) Alloys, dispersions (including cermets), ceramic products and mixtures containing these elements or isotopes or inorganic or organic compounds thereof and having a specific radioactivity exceeding 74 Bq/g (0.002 μCi/g); (e) Spent (irradiated) fuel elements (cartridges) of nuclear reactors; (f) Radioactive residues whether or not usable. The term “isotopes”, for the purposes of this Note and of the wording of headings 28.44 and 28.45, refers to : - individual nuclides, excluding, however, those existing in nature in the monoisotopic state; - mixtures of isotopes of one and the same element, enriched in one or several of the said isotopes, that is, elements of which the natural isotopic composition has been artificially modified. 7.- Heading 28.53 includes copper phosphide (phosphor copper) containing more than 15 % by weight of phosphorus. 8.- Chemical elements (for example, silicon and selenium) doped for use in electronics are to be classified in this Chapter, provided that they are in forms unworked as drawn, or in the form of cylinders or rods. When cut in the form of discs, wafers or similar forms, they fall in heading 38.18. Subheading Note. 1.- For the purposes of subheading 2852.10, the expression “chemically defined” means all organic or inorganic compounds of mercury meeting the requirements of paragraphs (a) to (e) of Note 1 to Chapter 28 or paragraphs (a) to (h) of Note 1 to Chapter 29.