Lead ore

“ It sometimes happens that lead ore or galena is discovered. Lead as a metal, except in very rare instances, is not found in a native or malleable form; and as the ore is a sulphuret, brittle, and easily pulverised, some method must be had recourse to in order to smelt and render it fit for use. Some Indians do it in the following manner:—After reducing a large quantity of the ore to powder, between heavy stones, they seek out a hollow tree stump, clear out the bottom flush with the ground, and dig a pit just outside it. ”

“ Lead ores of over seventy per cent. of metal are worked to obtain the required quantity of lead for bullet-moulding, and one lead ore which was sent me for assay contained a little over ten per cent. of silver. In the Sher Darwaza Heights is a vein of copper ore which runs throughout its length, outcropping here and there, but it is a thin seam and rather poor in metal, as compared with other ores round about, but the percentage is enough to pay handsomely for its working. ”

“ Lead, iron, coal, gypsum, manganese, zinc, antimony, cobalt, ochre of various kinds, common salt, nitre, plumbago, porphyry, jasper, chalcedony, buhrstone, marble, and freestone, of various qualities. The lead and iron ore are literally exhaustless, and of the richest quality. To say there is probably iron ore enough in this region to supply the United States with iron for one hundred thousand years to come, would not be extravagant. Here, too, is water power in abundance, rapid streams, with pebbly beds, forests of timber, and exhaustless beds of bituminous coal. ”

“ Lead-smelting is carried out both in reverberatory furnaces and in blast-furnaces. When galena, lead sulphide, the most common lead-ore, is obtained nearly pure, either directly from the mine or by concentration, it frequently is smelted by roasting it on the bed of a reverberatory furnace until it is partly changed to oxide and sulphate, then raising the heat to fusion and thus causing the oxidized part to act upon the remaining lead-sulphide with the formation of metallic lead and sulphur dioxide gas. ”

“ In the finer grades of tableware and decorative products lead takes the place of lime as the second base in the silicate, but with this material, again, America is well supplied. The immense deposits of lead ore in the Mississippi Valley, and the large output of the metal from the silver smelters of the West, make the supply of the oxide quite up to the demand. ”

“ The quantity of lead ore produced within the United Kingdom has decreased. It is now less than one-half of the output of about 1877, and the value has decreased more than proportionately. In the period 1890–1908 the maximum annual production of metallic lead from British ore Lead.was 33,590 tons in 1890, valued at £449,826; the production fluctuated somewhat, but generally fell, to the minimum of 17,704 tons in 1902 (value £198,875) . The most productive counties are Flint, Durham and Derby; the ore obtained in the Isle of Man is increased in value by the silver it contains. ”

“ Carbonates and sulphates of lead are less common. Solder and type metal are alloys of lead with tin and antimony. White lead is a carbonate, red lead and litharge are oxides. Chrome yellow and orange mineral are lead compounds used as pigments.
The chief use of metallic lead is in piping, sheet lead, shot and alloys. Large amounts of ore are transformed not into metallic lead but into white lead for use in paints. Lead ores and lead bullion are imported from Mexico. England is the greatest importer of lead and lead ores. ”

“ The ore may present visible metallurgical difficulties which make it unprofitable in any event. A gold ore may contain copper or arsenic, so as to debar cyanidation, where this process is the only hope of sufficiently moderate costs. A lead ore may be an amorphous compound with zinc, and successful concentration or smelting without great penalties may be precluded. ”

“ Ores of this type usually contain lead (galena) , zinc (sphalerite) , and iron (pyrite) minerals; many contain manganese and cadmium; some contain cobalt and nickel; but few carry gold, silver, copper, or antimony. Deposits of this type are of world-wide distribution, and many are extensive and commercially important. The greater purity of the ore and the simplicity of treatment (particularly [264] for the ores in the oxidized zones) , caused them to be exploited first and most extensively, and to dominate formerly the world production of lead. ”

“ The main sources of lead ore, named in order of their importance, are the United States, Australia, Spain, Germany, and Mexico, which account for over 80 per cent of the world's production. Most of the countries of Europe outside of Spain and Germany produce small amounts of lead, but are largely dependent on imports. ”

“ The comparative cheapness of lead, its admirable qualities, and the facility with which it can be cast and rolled into thin sheets, and drawn into pipes, cause it to be extensively used in building. The most productive mines of this metal in our own country are situated in Derbyshire, Devonshire, Cornwall, in Wales, and in the North; in short, the ore from which lead is generally obtained, called Galena, or Sulphuret of Lead, is found in all countries where the primary rocks appear at the surface. The ore greatly resembles the pure metal in brilliancy ”

“ The old method of producing white lead or carbonate of lead is one involving much time and labour, together with no small risk to the health of the workpeople. By the new process brought out by Mr. Hannay, sulphate of lead is manufactured direct from galena or lead ore, without the necessity of the intermediate process of the reduction of the ore and the extraction of metallic lead. It is said that the sulphate of lead produced by the new process is whiter and more permanent than the carbonate. ”

“ They are also harder to melt; and the lead obtained is not of so soft and malleable a nature as that procured from the broad-grained, easy-melting ore.
The proportion of silver in lead varies greatly. It is sometimes found to yield as high as twelve per cent., and is then called argentiferous lead-glance; but, in the poorest ores, it does not yield more than one ounce out of three hundred. To separate the silver from the lead, a process is pursued called the refining of lead, or cupellation. ”

“ In the Cœur d'Alene district of Idaho and the southeastern district of Missouri, the two greatest lead producers in the United States, the average grades are about 10 per cent and about 3-1⁄2 per cent respectively. The grade of ore which may be profitably worked depends not only upon the economic factors,—such as nearness to consuming centers, and the price of lead,—but also upon the amenability of the ore to concentration, the content of other valuable metals, and the fact that lead is very useful in smelting as a collector of gold and silver. ”

“ As the smelting of galena, the principal ore of lead, is not a little complex, the following tabular view of the different processes may prove acceptable to the metallurgist:—
The annual production of lead in Europe may be estimated at about 80,000 tons; of which four-sevenths are produced in England, two-sevenths in Spain, the remainder in Germany and Russia. France does not produce more than one five-hundredth part of the whole; and only one-fiftieth of its consumption.
See Litharge, Minium, or Red Lead, Solder, Sugar or Acetate of Lead, Type Metal, and White Lead. ”

“ The least fusible ores are generally the most difficult to smelt, and undergo the greatest loss in that operation. It is well known that a considerably greater produce of Lead can be obtained from the same ore after being properly roasted, than before. This difference is of course variable, but in some instances, 20 bings of roasted ore have yielded 8 or 9 cwt. more Lead than 20 bings of the same ore smelted in its raw state. ”

“ Almost at every smelting mill a different mode of working, in point of time and quantity, is pursued; in some cases the quantity of ore smelted in one hearth, in a week, by four men, is 40 bings; but a fair rate of working is from 30 to 35 bings per week.
The quantity of coal required to smelt a fodder of lead, as has been already stated, varies with the quality of the ore. ”

“ It stains paper or the fingers of a bluish colour, and is about eleven times heavier than water.
The most common state in which lead is found is in combination with sulphur and a small portion of silver. This ore is known by the name of galena, and is frequently in the form of blackish cubical crystals. Lead is also found in union with arsenic (242) and many acids.
Great Britain possesses the most important lead-mines in the world; and those that are best known are in the counties of Flint and Derby. ”

“ When metallic sulphides are present in the ore, an excess of oxide of lead helps to keep the sulphur out of the button of metal. In addition to the oxide of lead required as a flux, some will be required to provide the lead in which the silver is to be collected. Oxide of lead, mixed with charcoal or flour, yields, when heated, a multitude of minute buttons of metal uniformly distributed through the mass of the charge ”

“ To an hundred pounds of the Mineral, reduced into a small powder, add 8, 12, 16, or 18 pound of granulated Lead, or as much as the Mineral shall need, mix the Mineral and the powder of Lead, which with a little Spoon are to be committed to a fiery hot Cupel, placed under a Cineritium or Muffle, give a strong heat, and the Lead will attract all the metal from the Ore, and cast out the Scoria or dross, which will rest upon the moving Lead ”

“ The chief ore of lead is galena, a sulphide of lead, common in most mining districts, and frequently associated with blende and copper-pyrites. It always carries more or less silver; so that in the assay of the ore a silver determination is always necessary. ”

“ Silver may be separated from its ore, and at the same time refined, by the single operation of the cupel, without any previous scorification with Lead. In order to do this, you must pound the ore; roast it, to dissipate all its volatile parts; mix it with an equal quantity of litharge, if it be refractory; divide it into five or six parcels, wrapping each in a bit of paper; weigh out eight parts of granulated Lead for one of ore, if it be fusible, and from twelve to sixteen, if it be refractory; put one half of the Lead into a very large cupel under the muffle ”

“ A gentle warmth is created at first, which is raised very gradually, and kept at this point for about twelve hours, to allow the sulphur to dissipate; the heat is then increased for the purpose of smelting the ore, and, in twelve hours more, the operation is completed, and the lead obtained. Wood is occasionally added as the process goes on, and there is a practical nicety required in keeping the furnace in proper order, regulating the draught of air, &c., so that some smelters are much more expert, and thereby extract a greater quantity of lead from a like body of ore, than others. ”

“ Since then development has considerably increased these reserves. In addition there is estimated to be 1,600,000 tons of low-grade ore averaging 5.1 ounces of silver, 7.5 per cent. lead, 4.8 per cent. zinc, and 0.2 per cent. copper per ton, with excellent prospects of larger developments. A large tonnage of gossan outcrop ore containing 4 or 5 ounces silver, 4 to 5 per cent. lead, and a little zinc is cheaply mined and available as siliceous flux. The essential constituents of the ores are galena and sphalerite with a little pyrite and chalcopyrite. All of the ore is argentiferous. ”

“ When the lead melts and begins to oxidize, the lead oxide, or so-called litharge, combines with or dissolves the non-metallic and readily oxidizable constituents of the ore, while the gold and silver alloy with the lead. As the slag thus formed flows off to the sides of the scorifier, the assay clears and the melted metallic lead forms an “eye” in the middle. The door of the muffle is then opened and the current of air which is drawn over the scorifier rapidly oxidizes the lead, while the melted litharge gradually closes over the metal. ”

“ Such lead is thought to be a little harder, and some pretend to discover a lighter color.
The lead-ashes are reckoned to yield fifteen per cent. of lead (zane and all) , which, added to the first smelting, makes an average product of sixty-five per cent. This estimate will hold good uniformly, when the ores have been properly dressed, and the smelting well performed. Any spar adhering to the ore, renders it refractory; blende and pyrites have the same effect. The latter is particularly injurious, as it consists chiefly of sulphur; a substance known to render all ores refractory. ”

“ Another sample of 20 grams of the same ore, calcined, fused with 40 grams of nitre, and washed to ensure the removal of arsenic and sulphur, and treated according to the second method, gave a button weighing 5.27 grams, equalling 26-3/8 per cent. The ore contained a considerable quantity of lead. Lead renders the assay more difficult, since after calcination it remains as lead sulphate, and in the fusion for coarse copper reappears as a regulus on the button. ”

“ For although it should be mixed with Lead, the Minera of Lead, or Salt of Lead, yet they would not remain conjoin’d, but the Lead is easily melted, floweth, and leaveth the Ore, which by strong blowing is reduced into Scoria, retaining much gold, which so is lost, as well as the other which flew away in smoak, and at the best but a very little saved, which hath entred the Lead. ”