Potassium chloride, a fertilizer known as potash for short, is commonly found as a salt mineral and is extracted underground by mining methods. In Germany the crude potash salt often contains magnesium salts. The magnesium nutrient is contained in many single potash fertilizers, making them even more valuable. Magnesium is a constituent of the chlorophyll essential for photosynthesis and is also very important for the phosphorous balance of plants. It is needed to break down the organic substance in the soil, improving the soil structure. A large number of soils currently suffer from a more or less acute deficit of magnesium. Adequate supply of soils with magnesium is therefore a problem that must be urgently solved as the magnesium content of the potash salts is no longer adequate. For this purpose, besides magnesium carbonate and dolomite rocks that contain magnesium carbonate, kieserite (Mg[SO4] · H2O) is an increasingly popular alternative. Kieserite has a crystalline structure, is produced in a fine-grained form, is abrasive and has a Mohs hardness of 3.5.
K+S KALI GmbH, with production sites in Germany (Fig. 1) and France, specializes in the extraction, processing and utilization of potassium and magnesium salts and extracts 8.7 million t crude salt every year at the site near Wintershall. From kieserite, the company produces a sulphatic magnesium and sulphur fertilizer with 25 % water-soluble magnesium oxide and 20 % watersoluble sulphur. The main application is in combating chlorosis, a deficiency syndrome suffered by agricultural crops. Kieserite is approved for use in ecological farming.
In March 2007, Hosokawa Alpine received an order from K+S KALI to replace three old mills with one large, high-capacity turn-key grinding mill and classifier that can be run in 24-h operation to produce an annual output of 550 000 t kieserite with a fineness of 90 % < 90 µm. The supplied plant went into operation in January 2009. It comprises the largest Super Orion ball mill (Fig. 2) that Hosokawa Alpine has ever built: a wear-protected SO 400/500 steel ball mill with a weight of approx. 250 t, a motor power of 1 300 kW, 5.5 kV, equipped with sliding bearing system, slotted wall and neck journal discharge. The ball mill is operated in a closed circuit with a Stratoplex 1800 ASP air-swept classifier and two KAZ 2500 cyclones. The air circulation rate of the classifier is around 100 000 Bm³/h. The cyclones have a diameter of 2.5 m and height of 9.5 m and, like the classifier, are lined with hard metal (Fig. 3). The scope of supply included four bucket conveyors, each with a height of around 25 m, three troughed chain conveyors, each measuring 30 m in length, and a proportioning belt weigher with a width of 1 m. With a value < 1.5 mg/Bm³/h for the residual dust content verified and attested by TÜV-Sued, the dust collection system also included in the € 4-million contract ensures much better air purification than the residual dust content of < 10 mg/m³ specified by K+S.
The good cooperation, fast processing of the project and the results achieved with the supplied plant and with which the specified targets can be met have prompted K+S KALI to entrust Hosokawa Alpine with a new project: a plant for the production of kieserite at its Neuhof-Ellers site. For this application, Hosokawa Alpine has proposed the supply of a 1500 AWM table roller mill.
HOSOKAWA ALPINE AG, Augsburg (D), Dipl.-Ing Jörg Eisold,
Tel.: +49 821-5906-0, www.alpinehosokawa.com