Separation of ulexite from colemanite by thermally assisted comminution and screening
S. Şener
Mersin Üniversitesi, Mersin, Turkey
G. Özbayoğlu
Middle East Technical University, Ankara, Turkey

ABTRACT: Under beat treatment, some mİneralogical and structural changes take place in hydrated boron minerals Ulexite and colemanite lose their crystal water when they are subjected to heat treatment. Heat treatment significantly affects the grindability of ulexite and colemanite.

Thermal treatment followed by semiautogenous grinding and screening have been used for the separation of ulexite from colemanite. From an 1:1 artificial mixture of ulexite and colemanite calcined at 280°C, ulexite could be concentrated with 90,83 % recovery.
ÖZET: Isıl işlemler altında bazı bor mineralleri mineralojik ve yapısal değişikliğe uğrarlar. Uleksit ve
kolemanit ısıtıldıklarında kristal sularını kaybederler. Isıl işlemler, uleksit ve kolemanitin Öğütülebilirligİni
yakından etkilemektedir. Isıl İşlemler ve bunu takip eden yan-otojen öğütme ve eleme işlemleri uleksit ve
kolemanitin birbirinden ayrılmasında kullanılmıştır. 1:1 oranında karıştırılan uleksit ve kolemanitin 280°C'de
kalsinasyonlan sonucunda uleksit, %90,83 randımanlı kolemanitten ayrılabilmiştir.

1. INTRODUCTION

Al] hydrated boron minerals give of their water ofcrystallization on heating. The differential thermalanalyses (D.T.A) of selected borates were studied byAllen (1957). He found that all the mineralsinvestigated yielded distinctive endothernuc curvesbetween 50°C and 650°C. Colemanite, whoseendothermic reactions begins at 270°C, decrepitatesviolently between 350°C and 400°C, while in ulexite,endothermic reactions vary between 70°C and 200°C.Allen also studied artificial mixtures of colemaniteand ulexite and he used DTA curves for practicalsemi-quantitative analysis of these minerals.Şener (1997) found that thermal decomposition ofulexite has occurred within the temperature range of60-500°C with two stage dehydration proceeded withtwo-stage dehydroxylation giving two endothermicDTA peakes at 151° and 180°C.U.S. patent taken by Gnswold (1970) aboutcalcination of colemanite in a fluidised bed furnaceshowed mat the feed should be charged to the furnaceat 350°C for an efficient decrepitation. The powderedcalcine could be recovered in cyclone with 80%recovery.Industrial scale colemanite calcination is carriedout in the U.S.A. The American Borate Company hasused a rotary kiln to upgrade the B2O3 percent from22 % to 36%, and the calcine is separated from theassociated gangue by air cyclones. Lyday (1985).The aim of this research was to use the calcinationbehaviour of boron minerals for their separation.

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Separation of ulexite from colemanite by thermally assisted comminution and screening