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26.21 Other slag and ash, including seaweed ash (kelp); ash and residues from the incineration of municipal waste.
This heading covers slag and ash not falling in heading 26.18, 26.19 or 26.20, derived from the working of ores or from metallurgical processes, as well as those derived from any other material or process. Although many of the products are used as fertilisers they are classified here and not in Chapter 31 (except in the case of basic slag).
The products covered include :(1) Ash and clinker of mineral origin produced primarily from burning coal, lignite, peat or oil in utility boilers. Its principal uses are as a raw material for cement manufacture, as a supplement to cement in concrete, in mine backfill, as a mineral filler in plastics and paints, as a lightweight aggregate in building block manufacture and in civil engineering structures such as embankments, highway ramps and bridge abutments. It includes : (a) Fly ash ? finely divided particles entrained in furnace flue gases and removed from the gas stream by bag or electrostatic filters; (b) Bottom ash ? more coarse ash removed by settlement from the gas stream immediately after leaving the furnace; (c) Boiler slag ? coarse residues removed from the bottom of the furnace; (d) Fluidised bed combustor ash (FBC-ash) - inorganic residues from burning coal or oil in a fluidised bed of limestone or of dolomite. (2) Kelp and other vegetable ash. Kelp covered by this heading is material produced by incinerating certain types of seaweed. In its raw state it is a heavy, rough, blackish material but, when refined, it is a dull white powder. It is mainly used for extracting iodine or in the glass industry.
This group also includes rice husk ash, composed almost entirely of silica, and used primarily for the manufacture of sound insulating bricks or other sound insulating products. (3) Bone ash obtained from the calcination of bones in the open air. Apart from its use for soil improvement, this product is also used for coating ingot moulds in copper smelting. The heading excludes animal black, obtained from the calcination of bones in a closed vessel (heading 38.02). (4) Crude potassium salts obtained in the sugar industry from residues of beet molasses by incineration, washing, etc. (5) Ash and residues resulting from the incineration of municipal waste (see Note 4 to Chapter 38).
Such ash and residues are frequently a mixture of clinker and some toxic metals (e.g., lead) and generally used for the construction of temporary roadways on landfill sites as a substitute for aggregates. Metal content of this type of ash and residues does not warrant the recovery of metals or metal compounds.
The heading excludes separate chemically defined silica fume collected as a by-product from silicon, ferrosilicon and zirconia production, generally used as a pozzolanic additive in concrete, fibre cement, or refractory castables, and as an additive in polymers (heading 28.11).
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