Türk kolemanitlerinin termal elektrolizi ile kalsiyum hekzaborür eldesi

Abstract

Ill ÖZET Emet ve Bigadiç'ten sağlanan kolemanit minerali (2Ca0.3B203. 5HpO) örneklerinin kimyasal analizi, atomik absorbsiyonu, İR ve X-ray spektrumları alınarak bu örneklerin kolemanit yapısında olduğu kanıtlandı. örnekler kırılma, eleme ve dehidratasyon operasyonlarına tabi tutuldu. Elde edilen analiz sonuçları ve dehidratasyon bul guları Emet kökenli kolemanit örneklerinin, Bigadiç kökenli ör neklere göre içlerinde elektroliz açısından istenmeyen bazı gayrı safiyetler (Fe203, Si02, AlgOo, MgO ve SrÖ) içerdiğinden, elek troliz işlemleri Bigadiç kökenli anhidrit hale getirilmiş kolema nit örneklerine uygulandı. Bigadiç kökenli saf anhidrit kolemanit (2Ca0.3B203) ile anhidrit kalsiyum klorür (CaCl2) belli oranlarda karıştırılarak 900°C ile 1100°C arasında 150 dakika süre ile uygulanan 6-7 volt luk bir gerilim ve 20 amperi i k bir akım altında grafit pota (ka tot) ve grafit çubuk (anot) kullanılarak elektroliz edildi. Pota nın duvarlarında ve dibinde toplanan siyah renkli parlak, kristalIV manzarası görünümünde ve fakat kristal olmayan ürün, pota sıcak iken kazınarak alındı. Kazınarak alınan katot ürünü, hidroklorik asit (HC1) ile ekstrakte edildi. Daha sonra bu madde çeşitli çözücülerle mua mele edilip yıkandıktan sonra, bir etüve alındı. 110°C'da bir gece etüvde bekletilen madde iyice kuruduktan sonra, İR, atomik absorbsiyon ve klasik kimyasal analizlerine tabi tutuldu. Söz konusu maddenin kalsiyum hekzaborür (CaBg) yapısında olduğu sap tandı. Bu sonuca dayanarak, çalışmada uygulanan elektroliz yönte mi ile kalsiyum hekzaborür (CaBg) üretiminde olduğu gibi; Türki ye'deki diğer bor minerallerinden farklı metal borürl erinde üretiminin gerçekleştirilebileceği kanısına varılmıştır.

SUMMARY ELECTROCHEMICAL PRODUCTION OF CALCIUM BORIDE FROM TURKISH COLEMANITE The colemanite and tincal reserves together comprise the major part of the boron mineral deposits of Turkey, Since there are large deposits of colemanite which is a mineral having the composition represented by 2Ca0.3B203.5H20 in Emet and Bigadiç. It was worthwhile to investigate the electrolytic product of the calcium boride (CaBg) which has an increasing industrial impor tance. Calcium boride (CaBg) has recently found some important commercial applications, being used chiefly in the deoxidation of copper and other nonferrous alloys it is also a convenient source of boron for the preparation of other metallic borides and of boron alloys, as elemental boron. Colemanite mineral samples were taken from the vein near the country of Emet in the Kütahya province and near the country of Bigadiç in the Balıkesir province are subjected to X-Ray, IRVI and chemical analyses by atomic absorption spectrometry. 3 g. of each colemanite sample, ground in order to pass 80 mesh, was first dehydrated for 2 hrs at different tempera tures and optimum conditions for the dehydration was determined. 200°C, 300°C, 400°C 500°C and 550°C degrees for hours periods and at the end of e//ery 15 minutes dehydrated samples were weighed. It was found that at at 550°C samples were reached to constant-weight and at this temperature percentage of the loss of water was found to be 21,88 %. This result was in good agreement with theoretical value of 21,91 % which is calculated from 2Ca0.3B203.5H20. The dehydrated colemanite samples were subjected to elemen tal, IR and X-ray analyses. For the electrolytic production of calcium boride, an electric resistance furnace was initially designed a graphite crucible was placed in the furnace as a cathode, and graphite electrodes were used as anode. In some experiments, a small -scale' electrolytic cell was used. The dehydrated colemanite samples were electrolysed between 900-1 100°C in the presence of calcium chloride which lower the melting point. The portions of colemanite samples were added periodically to the cell during the course of the electrolyses.VII The best operating conditions for the electrolysis of calcium boride (CaBg) were as follows : To determine optimum conditions of bath composition, electrolysis was carried out with several different bath compositions of colemanite and calcium chloride (CaClo). The reactions taking place during the electrolysis may be indicated as follows : (I) (2) (3) 10 CaO 10 Ca+3 B203 10 C+5 02 hMO Ca +5 02 -»»CaBg 4- 9 CaO -^10 CO The calcium chloride (CaCl2) takes no part in the reaction and is utilized merely as a flux and to increase the fluidity and conductivity of bath.VIII It will be noted from reaction (2) that a considerable amount of calcium oxide (CaO) is formed at the cathode. After the completion of each electrolysis experiments, the contents of cell were leached and extracted with hydro chloric acid (HC1) to remove calcium oxide (CaO), Boron oxide (BpOo) and calcium chloride (CaClp). Black and brilliant crystals which were obtained after extraction processes, washed with water, ethanol and ether and later they were dried in an oven at 110°C degrees for 24 hours. The yield was found to be 42% from the following eguation. Yield product ; M.I. t m = Z.F in this eguation,.1 m s= Amount of calcium hexzaboride deposited of the cathode. M= Number of moles of calcium hexzaboride deposited of cathode. Z = Number of electrons transferred. I =Total amount of current pasied through electrolyte, t «Electrolysis time F ;=Fara.«lay constantsIX According the faraday law, M.I. t m theoretical ~` Z.F m n = experimental x 100 m theoretical This product was subject to elemental and IR analyses. The result of chemical analyses of electrolysis product calcium hexzaboride (CaBg) and of dehydrated colemanite mine ral are summarized in the following table. As a result of this investigation, it was concluded that a high grade of calcium boride (CaBg) from Turkish colemanite (Bigadiç) can be produced at relatively low temperatures by this method, and other Turkish boron minerals could also be used as raw materials for the production of other metal borides,