POTASH IN MINERAL DEPOSITS.
235. Occurrence and History.—The generally accepted theory of the manner in which potash has been collected into deposits suited to use as a fertilizer has already been described.[194] The Stassfurt deposits, which have for many years been almost the sole source of potash in fertilizers, were first known as mines of rock salt. In 1839, having previously been acquired by the Prussian treasury, they were abandoned by reason of the more economical working of rock salt quarries in other localities.[195] It was determined thereafter to explore the extent of these mines by boring, and a well was sunk to the depth of 246 meters, when the upper layer of the salt deposit was reached. The boring was continued into the salt to a total depth of 581 meters without reaching the bottom. The results of these experiments were totally unexpected. Instead of getting a brine saturated with common salt, one was obtained containing large quantities of potassium and magnesium chlorids.[196] Shafts were sunk in other places, and with such favorable results, that in 1862 potash salts became a regular article of commerce from that locality. At first these salts were regarded as troublesome impurities in the brine from which common salt was to be made, but at this time the common salt has come to be regarded as the disturbing factor. At the present time the entire product is controlled by a syndicate of nine large firms located at Stassfurt and vicinity. Outside of the syndicate properties a shaft has been sunk at Anderbeck, (Halberstadt,) which, however, has produced only carnallit, since kainit has not been found there. Also at Sondershausen, potash salts have been discovered and a shaft is now sinking there.
It is thus seen that the potash deposits extend over a wide area in Germany, and there is little fear of the deposits becoming exhausted in many centuries. In this country no potash deposits of any commercial importance have been discovered; but the geological conditions requisite to these formations have not been wanting, and their future discovery is not improbable.
Figure. 17.
Geological Relations of the Potash
Deposits near Stassfurt.
236. Changes in Potash Salts in Situ.—The deposits of potash salts are not all found at the present in the same condition in which they were first deposited from the natural brines. The layers of salt have been subjected to the usual upheavals and subsidences peculiar to geological history. The layers of salt were thus tilted and the edges often brought to the surface. Here they were exposed to solution, and the dissolved brine afterward separated its crystallizable salts in new combinations. For instance, kieserit and the potassium chlorid of the carnallit were first dissolved and there was left a salt compound chiefly of potassium and sodium chlorids, sylvinit. In some cases there was a mutual reaction between the magnesium sulfate and the potassium chlorid and the magnesium potassium sulfate, schönit, was thus produced. This salt is also prepared at the mines artificially. The most important of these secondary products however, from the agricultural standpoint, is kainit. This salt arose by the bringing together of potassium sulfate, magnesium sulfate, and magnesium chlorid, and was formed everywhere about the borders of the layers of carnallit wherever water could work upon them. In quantity the kainit, as might be supposed, is far less than the carnallit, the latter existing in immense deposits. There is however quite enough of it to satisfy all the demands of agriculture for an indefinite time. In fact for many purposes the carnallit can take the place of kainit without detriment to the growing crops. The relative positions and quantities of the layers of mineral matters in the potash mines, and the depth in meters at which they are found is shown in [Fig. 17].[197]
237. Kainit.—The most important of the natural salts of potash for fertilizing purposes is the mixture known as kainit. It is composed in a pure state of a molecule each of potassium sulfate, magnesium sulfate, magnesium chlorid, and water. Chemically it is represented by the symbols:
K₂SO₄·MgSO₄·MgCl₂·H₂O. Its theoretical percentage of potash (K₂O), oxygen = 16, is 23.2.
Pure kainit, however, is never found in commerce. It is mixed naturally as it comes from the mines with common salt, potassium chlorid, gypsum, and other bodies. The content of potash in the commercial salt is therefore only a little more than half that of the pure mineral. In general it may be taken at 12.5 per cent, of which more than one per cent is derived from the potassium chlorid present. The following analysis given by Maercker may be regarded as typical:[198]
| Potassium | sulfate | 21.3 | per cent | |
| Magnesium | “ | 14.5 | “ | |
| Magnesium | chlorid | 12.4 | “ | |
| Potassium | “ | 2.0 | “ | |
| Sodium | “ | 34.6 | “ | |
| Calcium | sulfate | (gypsum) | 1.7 | “ |
| Water | 12.7 | “ | ||
| Alumina | 0.8 | “ | ||
Kainit occurs as a crystalline, partly colorless, partly yellow-red mass. When ground, in which state it is sent into commerce, it forms a fine, gray-colored mass containing many small yellow and red fragments. It is not hygroscopic and if it become moist it is due to the excess of common salt which it contains.
According to Maercker kainit was formerly regarded as a potassium magnesium sulfate. But this conception does not even apply to the pure salt much less to that which comes from the mines. If, therefore, the agronomist desire a fertilizer free from chlorin he would be deceived in choosing kainit which may sometimes contain nearly fifty per cent of its weight of chlorids.
Where a fertilizer free of chlorin is desired, as for instance, in the culture of tobacco, kainit cannot be considered. In many other cases, however, the chlorin content of this body instead of being a detriment may prove positively advantageous, the chlorids on account of their easy diffusibility through the soil serving to distribute the other ingredients.
By reason of the presence of common salt and magnesium chlorid the ground kainit delivered to commerce tends to harden into compact masses. To prevent this in Germany it is recommended to mix it with about two and a half per cent of fine-ground dry peat.
Such a mixture is recommended in all cases where the freshly ground kainit is not to be immediately applied to the soil.
238. Carnallit.—This mineral is a mixture of even molecules of potassium and magnesium chlorids crystallized with six molecules of water. It is represented by the symbols KCl·MgCl₂·6H₂O. As it comes from the mines it contains small quantities of potassium and magnesium sulfates and small quantities of other accidental impurities. Existing as it does in immense quantities it has been extensively used for the manufacture of the commercial potassium chlorid (muriate of potash). For many purposes in agriculture, for instance, fertilizing tobacco fields, it is not suited, and it is less widely used as a fertilizer in general than its alteration product kainit. Its direct use as a fertilizer however is rapidly increasing since later experience has shown that chlorin compounds are capable of a far wider application in agriculture without danger of injury than was formerly supposed. As it comes from the mines, the Stassfurt carnallit has the following composition:[199]
| Potassium | chlorid | 15.5 | per | cent. |
| Magnesium | “ | 21.5 | “ | “ |
| Magnesium | sulfate | 12.1 | “ | “ |
| Sodium | chlorid | 22.4 | “ | “ |
| Calcium | sulfate | 1.9 | “ | “ |
| Water | 26.1 | “ | “ | |
| Undetermined | 0.5 | “ | “ | |
Pure carnallit would have the following composition:
| Chlorin | 38.3 | per | cent. |
| Potassium | 14.0 | “ | “ |
| Magnesium | 8.7 | “ | “ |
| Water | 39.0 | “ | “ |
Equivalent to
| Potassium | chlorid | 26.8 | “ | “ |
| Magnesium | “ | 34.2 | “ | “ |
| Water | 39.0 | “ | “ | |
The commercial article as taken from the mines, as is seen above, has less potash (K₂O) than kainit, the mean content being about nine and nine-tenths per cent. Those proposing to use this body for fertilizing purposes should bear in mind that it contains less potash and more chlorin than kainit.
Carnallit occurs in characteristic brown-red masses. On account of its highly hygroscopic nature it should be kept as much as possible out of contact with moist air and should not be ground until immediately before using.
By reason of the greater bulk in proportion to its content of potash and its hygroscopic nature and consequent increased difficulty in handling, the price per unit of potash in carnallit is less than in kainit.
In some localities small quantities of ammonium chlorid have been found with carnallit but not to exceed one-tenth per cent. It has therefore no practical significance to the farmer but may be of interest to the analyst.
239. Polyhalit.—Polyhalit is a mineral occurring in Stassfurt deposits and consisting of a mixture of potassium, magnesium, and calcium sulfates, with a small proportion of crystal water. This mineral, on account of its being practically free of chlorin, would be one especially desirable for use in those cases, as in the culture of tobacco, where chlorids are injurious. Unfortunately, it does not occur in sufficient quantities to warrant the expectation of its ever being found in masses large enough to become a general article of commerce. It is found only in pockets or seams among the other Stassfurt deposits, and there is no assurance given on finding one of these deposits of polyhalit that it will extend to any great distance. The composition of the mineral is shown by the following formula: K₂SO₄·MgSO₄·(CaSO₄)₂·H₂O. Its percentage composition is shown by the following numbers:
| Potassium sulfate | 28.90 | per | cent. |
| Magnesium sulfate | 19.93 | “ | “ |
| Calcium sulfate | 45.18 | “ | “ |
| Water | 5.99 | “ | “ |
The percentage of potash corresponding to the above formula is 15.62. It therefore contains a considerable excess of potash over kainit, and on account of its freedom from chlorids, would be preferred for many purposes.
240. Krugit.—This mineral occurs associated with polyhalit and differs from it only in containing four molecules of calcium sulfate instead of two. Its formula is: K₂SO₄·MgSO₄·(CaSO₄)₄·H₂O. As it comes from the mines it is frequently mixed with a little common salt. Its mean percentage composition as it comes from the mines is given in the following numbers:
| Potassium sulfate | 18.60 | per | cent. |
| Magnesium sulfate | 14.70 | “ | “ |
| Calcium sulfate | 61.00 | “ | “ |
| Sodium chlorid | 1.50 | “ | “ |
| Water | 4.20 | “ | “ |
The percentage of potash corresponding to the above formula is 10.05. It is therefore less valuable than kainit in so far as its content of potash is concerned. This salt also exists in limited quantities and is not likely to become an important article of commerce.
241. Sylvin.—One of the alteration products of carnallit is a practically pure potassium chlorid which, as it occurs in the Stassfurt mines is known as sylvin. The alteration of the carnallit arises from its solution in water from which, on subsequent evaporation, the potassium chlorid is deposited alone. This mineral is found in only limited quantities in the Stassfurt deposits and it therefore does not have any great commercial importance.
242. Sylvinit.—This mineral has been mined in recent years in considerable quantities. It is, in fact, only common salt carrying large quantities of potassium chlorid together with certain other accidental impurities. It was probably formed by the drying up of a saline mass in such a way as not to permit the complete separation of its mineral constituents. The average composition of sylvinit as it comes from the mines is given in the following table:
| Potassium chlorid | 30.55 | per cent. |
| Sodium chlorid | 46.05 | “ |
| Potassium sulfate | 6.95 | “ |
| Magnesium sulfate | 4.80 | “ |
| Magnesium chlorid | 2.54 | “ |
| Calcium sulfate | 1.80 | “ |
| Water and insoluble | 7.29 | “ |
This salt is richer in chlorin than any other of the Stassfurt potash minerals, containing altogether 79.14 per cent of chlorids. Its potash content amounts to 23.04 per cent, but in proportion to the potash which it contains, it is relatively poorer in chlorin than kainit and carnallit. On account of its high content of potash the freights on a given weight thereof as contained in sylvanit are lower than for kainit and carnallit.
243. Kieserit.—The mineral kieserit is essentially magnesium sulfate and it does not necessarily contain any potash salts. Under the name of kieserit, however, or bergkieserit, there is mined a mixture of carnallit and kieserit, which is a commercial source of potash. The mixture contains the following average content of the bodies named:
| Potassium chlorid | 11.80 | per cent. |
| Magnesium sulfate | 21.50 | “ |
| Magnesium chlorid | 17.20 | “ |
| Sodium chlorid | 26.70 | “ |
| Calcium sulfate | 0.80 | “ |
| Water | 20.70 | “ |
| Insoluble | 1.30 | “ |
This mixture contains only about seven per cent of potash and would not prove profitable when used at a distance from the mines on account of the cost of freights. It has proved valuable, however, for a top dressing for meadow lands in the vicinity of Stassfurt.
244. Schönit.—Among the Stassfurt deposits there occurs in small quantities a mineral, schönit, which is composed of the sulfates of potassium and magnesium. The quantity of the mineral occurring naturally is very small and therefore it has no commercial importance. When, however, kainit is washed with water the common salt and magnesium chlorid which it contains being more soluble are the first leached out, and the residue has approximately the composition of the pure mineral. This mixture, as prepared in the way mentioned above, has the following average composition:
| Potassium sulfate | 50.40 | per cent. |
| Magnesium sulfate | 34.00 | “ |
| Sodium chlorid | 2.50 | “ |
| Water | 11.60 | “ |
The percentage of potash corresponding to the above composition is 27.2. This substance being so rich in potash, and practically free of chlorids, is well suited to transportation to great distances and for general use in the field. Since, however, a considerable expense attends the manufacture of the artificial schönit, the advantages above named give it very little, if any, advantage in competition with the other potash salts as they come from the mines. It has, however, an especial value for the fertilization of tobacco and vineyards.
245. Potassium Sulfate.—Several grades of potassium sulfate are found in the market for fertilizing purposes, some of them quite pure, containing over ninety-seven per cent of the pure sulfate. The following data show the composition of a high grade and low grade potassium sulfate of commerce:
| High grade. | Low grade. | |||
| Potassium sulfate | 97.20 | per cent. | 90.60 | per cent. |
| Potassium chlorid | 0.30 | “ | 1.60 | “ |
| Magnesium sulfate | 0.70 | “ | 2.70 | “ |
| Magnesium chlorid | 0.40 | “ | 1.00 | “ |
| Sodium chlorid | 0.20 | “ | 1.20 | “ |
| Insoluble | 0.20 | “ | 0.30 | “ |
| Water | 0.70 | “ | 2.20 | “ |
Naturally, high grade sulfates of this kind can only be prepared in chemical factories built especially for the work. The result is that the potash per unit is raised greatly in price. When, however, the fertilizers are to be transported to a great distance, the saving in freight often more than compensates for the higher price of the potash. It therefore happens that there are many places in this country where the actual price of potash per pound is less in high grade sulfates than in kainit or carnallit. When, in addition to this, the especial fitness of the high grade sulfates for certain forms of fertilization, especially tobacco growing, is considered, it is seen that at this distance from the mines these high grade salts are of no inconsiderable importance. The percentage of potash in the high grade sulfates often exceeds fifty.
246. Potassium Magnesium Carbonate.—This salt has lately been manufactured and used to a considerable extent, especially for tobacco fertilizing. As furnished to the trade it has the following average composition:
| Potassium carbonate | 35 to 40 | per cent. |
| Magnesium carbonate | 33 to 36 | “ |
| Water of crystallization | 25 | “ |
| Potassium chlorid, potassium sulfate, | ||
| and insoluble | 2 to 3 | “ |
The content of potash, as is seen from the above formula, amounts to from seventeen to eighteen per cent. The compound is completely dry, is not hygroscopic, and is, therefore, always ready for distribution. It is especially to be recommended for all those intensive cultures where it is feared that chlorids and sulfates will prove injurious, especially in the cultivation of tobacco.
247. Potash in Factory Residues.—The residues from the potash factories in Stassfurt and vicinity contain considerable quantities of potash and attempts have been made to recover this waste and put it into form for fertilizing uses. The waste waters of the factories are sometimes collected and evaporated, and the residue incinerated. The content of potash in these residues is extremely variable, usually quite low, and they, therefore, cannot be recommended for fertilizing purposes, especially if they are to be transported to any distance.
248. Quantity of Potash Salts Used.—The total quantity of potash delivered to consumers from the Stassfurt mines in 1891, the last year for which complete statistics are at hand was 413,508 tons of kainit and sylvinit, 39,444 tons of carnallit, 18,078 tons of sulfate, and 12,453 tons of the potassium magnesium sulfate. Of the above quantities, 115,245 tons of kainit were shipped to North America, and of the high grade sulfate mentioned, 13,322 tons were sent to other countries, and of the potassium magnesium sulfate, 11,081 tons were exported.