تجارب مختبرية لتنقية الدولومايت من الحديد بالطرق الفيزيائية

Abstract

Summary This work refers to a process for obtaining Dolomite of low content of iron (Fe2O3%). Different processes were used for this purpose, wet grinding, scrubbing, and dispersion by using EDTA as dispersing agent. Wet grinding and scrubbing at optimum conditions (solid 75%, scrubbing time 10 min. and 1000 r.p.m ) decrease the iron content from (0.27% to 0.1%) while dispersion process never decrease the (Fe2O3% ) .

Keywords :- Dolomite, scrubbing , iron content , dispersion .

Introduction Dolomite (Dolostone) is a double carbonate of calcium and magnesium , (CaCO3 , MgCO3). Dolomite deposits are usually associated with limestone (CaCO3 ).This fact, together with the presence of variable amounts of impurities , such as silica , sulphur ,iron oxide and alumina, has an important bearing on the suitability of dolomite for specific application.Industrial dolomite is a commercial term for dolomite used for non – construction purposes where its chemical properties are important. Pure dolomite has an( MgO) content of about (40 %) . However, glass manufactures normally use pre-calcined (MgO) content for control purpose and there is theoretical maximum of about (21.8 %) MgO (David et al., 2006).In glass industry, the content of iron (Fe2O3) wt% in dolomite is very important that limit range of it is between (0.05) and (0.25 wt%) . Pigments derived from Dolomitic ores find application in a wide variety of industrial and other environments. Such pigments, for example, can be used as fillers in the manufacture of rubber, of various plastics, and as extenders in paints formulations. In many of the aforementioned applications, particularly e.g. where the pigments are to be used for paper production, it is desirable that they be as bright as possible. It is found that very many of the Dolomitic deposits are so highly contaminated with discolor ants, that when comminuted in their natural state they are simply unacceptable as pigments. Thus, in typical instances deposits which are primarily of Dolomitic limestone, may be contaminated with pyrites, hematite and with mica; all of which in varying degrees contribute to the discoloration of the otherwise relatively colorless material (Nott et al., 1976).

Experimental Work A crushed sample (-2mm) was washed with water upon sieve opening (1mm) to remove the accomplished clays from Dolomite. Purification of Dolomite from Iron includes different physical separation methods as follows: Wet Milling: Above mentioned sample was grounded in a laboratory ball mill to pass –(75μ) (wet milling), the ratio of dolomite to water to balls was (1:5:3) respectively. The resulted milled dolomite (-75) μ \ dried at temperature (100ºC) . Scrubbing of Dolomite: The resulted Dolomite from wet milling was scrubbed by using one cell conventional attrition scrubber (type Denver) with standard sand (-850+600) μ. The ratio of Dolomite to the sand was 1: 2 by weight, then the water was added to produce (75%) solid ratio. The scrubbing characteristics were investigated as function of scrubbing time (10, 15, and 20) min at different (r.p.m) values (500, 1000, and 1500).The slurry was screened on 212μ to remove the sand particles. The produced slurry was found above of (70%) less than (25μ). The slurry (-25μ) was dried in oven at (100ºC) and sent to chemical analysis. Dispersing of Dolomite : Samples of (scrubbed Dolomite -25 μ) were conducted in flask of 1 liter capacity. The slurry of 7.5%) was agitated at (2000 r.p.m) for (5 min) while maintaining (pH) value at (10) and different values of ethylene diamine tetra acetic acid E.D.T.A (0.05, 0.135, 0.22, 0.35, and 0.45)% was added to the slurry prior to agitation and re-agitated for (15 min) again. The sediments were dispersed using cylinder of (1L) then separated from suspension using centrifugal force by (Mod. Rotanta type 640) at ( 1000 r.p.m ) for (5 min).

Results and Discussion Effect of Wet Milling:The (Fe2O3) in the product was analyzed after passing it through sieve (75μ) which giving low value than the raw (0.13%).This good result due to the librating of the hematite contaminants during the milling (Alan J.Nott, 1976). Effect of Scrubbing :The scrubbing tests were conducted to achieve more libration to the mineral oxides and it was accomplished with using standard sand to achieve sever attrition to the dolomite. Two parameters were focused on them, the first one, effect of changing scrubbing time on minimize (Fe2O3%) , these tests were done at constant ( 1000 r.p.m) , solid (75%) , the results was shown in Figure (1), it was clear that (Fe2O3%) value was decreased when scrubbing time was increased to (15 min) . and beyond this the (Fe2O3%) value was fixed at the same value. However, effect of modifying (r.p.m) on (Fe2O3%) value was the second route and these tests were done at constant time (15 min). and solid (75%) (1 sand+ 2 Dolomite) , Figure (2) was summarized the results. It is obvious (Fe2O3 %) value was gradually decreased with increasing (r.p.m) and still close to be a constant value at( 1500 r.p.m) . Dispersion of Dolomite: Different concentration of ethylene diamine tetra acetic acid (E.D.T.A) was added to the scrubbed Dolomite (-25) μ (0.135, 0.22, 0.35, 0.45) % at constant pH=10, solid (75%) , dispersion time (15 min) , centrifugation time (5 min) with (r.p.m 1000) , (Fe2O3 %) in the non-dispersed product ( 0.1%) . At all these experiments, no suspended dolomite was noticed and all the particles were precipitated, the resulted analyses was shown in figure (3), it is clear when scrubbed dolomite is dispersed with EDTA (Fe2O3%) was decreased to (0.1%) then was increased with increasing EDTA % to (0.25%) and the level of (Fe2O3%) value was decreased with increasing EDTA% to (0.45%) , so that these results were unexpectable and random due to inaccurate analyses of atomic absorption spectrophotometer analyzer, thus, it was contracted with results of scrubbed Dolomite as shown in figure (1) so the other parameters were not studied.

References 1- David, H., Bioood worth, A. and Bate, R., 2006. Dolomite, British Geological Survey. Nott,A.J., 1976. Brightening of Natural Dolomitic Ores United State Patent 3,990,642. www.mineralszone.com /minerals/dolomite.html).

Fig.1: Effect of scrubbing time Fig. 2: Effect of scrubbing r.p.m on (Fe2O3%) value on (Fe2O3%) value

Fig.3: Effect of EDTA on (Fe2O3%) value