INJURY TO VEGETATION AND ANIMAL LIFE BY

SMELTER WASTES.

INTRODUCTION.

PROCESS OF EXTRACTING METALS FROM ORES.

Before considering the injurious effects which wastes from plants smelting sulphid copper ores may have on vegetation and animal life, a brief account will be given of the process generally used to extract the metal from the ores. For this purpose an outline of the process followed at Anaconda, Mont., will be given, which, though differing in some details from the process used at other plants, is based on the same general principles and produces similar waste products.

The ores when they arrive at the plant are graded as first and second class, the former being sent to the bins of the blast furnaces and the latter to the concentrator bins. The second-class ores are next sampled, crushed, and passed over jigs, by which process a product richer in copper, known as the "concentrates," is obtained.

The reject from the jigs is crushed again and passed over jigs fitted with finer screens, "concentrates" being again obtained. After extracting all that can be taken out by the jigs, the ore is again crushed and passed over the Wilfley tables, thus giving rise to the "table concentrates." The concentrates are sent to a bin at the foot of the concentrator. There remain in the water used for concentration some fine particles of valuable material, and this is allowed to flow into ponds outside the plant, where the fine particles settle out in the form of "slimes" and the water is finally drawn off. The slimes are briquetted and blast-smelted. The waste products from the concentration are known as " tailings." These tailings, consisting principally of silica, iron, etc., with small quantities of copper and arsenic, in case the latter is present, are discharged on the dump heap.

The concentrates are dumped into roasting furnaces, where large quantities of sulphur and arsenic are driven off, the former as sulphur dioxid and trioxid and the latter in volatile form. The residue, now known as "calcine," is transferred to reverberatory furnaces. This process yields (1) a slag consisting principally of silicates of iron and calcium with very small quantities of copper; (2) a product richer in copper known as "matte;" and (3) volatile

arsenic and sulphur products which are carried to the flue. The slag is granulated in water and passed to the dump. The "matte" is carried to the converters, where it is treated in the same way as "matte" from the blast furnaces.

The blast furnace receives a charge consisting essentially of the high-grade ores, converter slag, briquettes of siliceous fines and slimes from the concentrator, limestone, and coke. A large part of the sulphur passes off to the flue as sulphur dioxid and trioxid, and large amounts of arsenic are volatilized. The iron and silica in the ore, together with the lime, form a slag (containing a very small amount of copper) which is granulated in water and carried to the dump; the copper forms a "matte" consisting principally of a combination of copper, iron, and sulphur. This, together with the "matte" from the reverberatory furnaces, is next carried to the converters, the lining of which is a siliceous material that lasts for several runs.

In the converter the sulphur which is present in the "matte" is oxidized to sulphur dioxid and trioxid and escapes up the flue, the remaining arsenic is volatilized and also goes up the flue, while the iron unites with the siliceous lining to form a slag which is returned to the blast furnaces, since it is a good flux and also contains considerable quantities of copper. The copper obtained by this process is carried to the preliminary refining apparatus, where air is passed over the molten mass to remove traces of sulphur and the small amount of slag which was not taken out in the converters is also eliminated. During this process some copper oxid is formed, but upon stirring this is again reduced to copper by the carbon of the converter poles. In this condition the copper is cast into ingots, which are sold to refineries not situated at Anaconda.

The fumes from these processes are passed through long cooling chambers in order to condense the volatilized compounds of arsenic as far as possible, but in spite of this precaution large amounts of arsenic escape from the top of the chimney. No attempt is made to. recover any of the sulphur compounds.

RESULTANT WASTES.

From this brief description of the process used at Anaconda, it will be evident that four wastes arise which may be injurious to plant or animal life.

(1) The sulphur contained in the ore is gradually given off during the various processes of smelting, as sulphur dioxid and a little sulphur trioxid, which would have their injurious action on vegeta

KESWICK SMELTER, NEAR REDDING, CAL., IN OPERATION.

(2) In case arsenic is present in the ores, as it often is and notably at Anaconda, it is given off in the fumes from the smelter in volatile form and deposited on the surrounding land and crops, where it may be present in sufficient amounts to poison cattle browsing on exposed ranges, or living on hay cut from such pasture.

(3) The tailings from the water concentration of the ore and the slag, in a finely divided condition, are discharged on a dump heap through which the water from the plant is constantly percolating on its course to adjacent streams and the "slimes" are left in piles in the open air. Both the slime heap and the dump are also exposed to the percolating action of the rain. In consequence, the streams receiving the waste water from concentrating and smelting plants contain a comparatively large amount of copper in suspension and are apt to hold some copper in solution. If these streams are used for irrigating purposes there is a possible source of injury to growing crops due to the action of the copper present.

(4) Finely divided particles of the ore are discharged from the smelter stack and settle on the surrounding country. These fine particles of flue dust may contain sufficient amounts of copper, lead, and zinc to injure vegetation, because of their toxic action through the medium of the soil and because of their caustic action on the foliage. While it is believed by some that the action of this so-called flue dust gives rise to the principal damage caused by smelter smoke, the writer is inclined to the opinion that such injury is not of great significance except in a very limited area about the smelter, and that an investigation of it is in most cases unnecessary, as the owners of smelters are usually perfectly willing to admit damage, even beyond the area likely to be affected by the solid particles of copper, lead, and zinc in the flue dust.

b

In the first case of this kind studied by the writer in the vicinity of Redding, Cal. (see Pl. I), and in the laboratory at Washington during 1903 and 1904, no complaint had been made of the injury from arsenic or from copper, so that the only problem considered was the action of sulphur dioxid and trioxid fumes on the surrounding vegetation. The results of this study and the original investigations connected therewith have been published, but a résumé will be given, together with certain results obtained since the publication of the Redding investigations, in order that the reader may understand the present status of the work.

a Ebaugh, J. Amer. Chem. Soc., 1907, 29: 951. Haywood, Science, 1907, 26: 476.

CU. S. Dept. Agr., Bureau of Chemistry, Bul. 89, Injury to Vegetation by Smelter Fumes, 1905.

38816-Bull. 113-10- 2