REACTIONS IN INERT FUSED SUBSTANCES Production of Blanc Fixe from Barytes HAROLD SIMMONS BOOTH, ELISHA FREDERICK POLLARD'. AND MAHLON JACOB RENTSCHLER2 Western Reserve University, Cleveland 6 , Ohio T h i s investigation and pilot plant operation have established the practicality of production of pigment and medical grade blanc fixe by a process involving solution of barytes in molten salt; separation of impurities by settling; decolorizing the traces of impurities left; quenching the melt in water; washings filtering; and drying the product. This is the first of three articles, published in this isniir. on reactions in inert substances.
T
HE principal method heretofore used for the production of barium compounds consists of the furnace reduction of barytes by carbon t o the water-soluble sulfide. However, preparation of pure barium compounds from the aqueous solution of the wlfide is objectionable because of contamination with sulfur compounds. Blanc fixe (precipitated barium sulfate) has in part been produced as a by-product and in part by precipitation from barium sulfide solution. Production of this pigment in pure condition a t a lowered price would increase its use many times. Of the various possible procedures for producing blanc fixe from barytes, solution in fused salt seemed the most promising although the most unorthodox. iMoffatt (9) reported that barium sulfate is soluble in fused sodium chloride and that on quenching the melt in water, the barium sulfate is repreaipitated. However, the product was tinted a faint pink. EXPERIMENTAL
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Preliminary experiments corroborated Moffatt's report that d l but a trace of impurities could be removed from barytes by solution in fused salt, settling, and decantation. Since it was suspected that the faint pink color was due to suspended iron oxide, the melted decantate was filtered through a platinum Monroe Gooch crucible with platinum felt, maintained a t about 1000" C. The molten filtrate solidified to a pure white product which on leaching with water to remove the salt gave a pure white barium gulfate. The coloring matter separated by this process proved to be iron oxide. Because of the impracticality of filtering molten salt on a large scale, many experiments looking toward removal of the iron oxide mere tried. Bubbling airborne carbon tetrachloride up through molten decantate removed some of the iron as ferric chloride. Tried in a similar way, hydrogen chloride removed no iron. It had been observed that most of the gangue settled out as an iron silicate which suggested the addition of silica to the molten decantate. This quickly cleared up the melt and the resultant barium sulfate was white. Sodium disilicate did not lighten the color. Although the addition of borax cleared the melt, the barium sulfate developed a pink color on digestion with water. 1 Present address, Southern Regional Research Laboratory, U. S. Departrlient of Agriculture, New Orleans, La. * Present address. Barium & Chemicals, Inc., Willoughby, Ohio
As none of these procedures was entirely satisfactory, conversion of the iron oxide impurity to a colorless or blue iron salt was tried. Inasmuch as iron phosphate is practically colorless, the addition of sodium acid phosphate to the decantate was tried with the result that a pure blue-white barium sulfate was produced on quenching the melt in water. It was found that the molten decantates were cleared and a pure white barium sulfate was produced when the following were added to the melt in small amounts: disodium phosphate, trisodium phosphate, primary calcium phosphate, secondary calcium phosphate, tertiary calcium phosphate plus sodium hydrogen sulfate, ammonium phosphates, tertiary barium phosphate plus sodium hydrogen sulfate, and commercial superphosphate fertilizer (1). Continuous boiling of the barium sulfate, whitened in this manner by phosphates, effected no change in the whiteness of the product. Blanc fixe made in this way and kept in barrels hae shown no change in 10 years. COMMERCIAL APPLICATION O F THE PROCESS
The conversion from platinum crucible to pilot plant scale producing 50 tons per day was solved m( e easily than expected. Fortunately, the cheapest grade of firebi ck liner was found eminently satisfactory to resist the reaction of fused salt. The heart of the process is the furnace design (5). DESCRIPTION OF FURNACE
The furnace shown in Figures 1 , 2 , and 3 was made of a 10-foot long welded steel shell, 0.5 inch thick, lined 9 inches thick with an all-clay firebrick. The poorest grade of firebrick waB found to be the best for this use. Neither silica brick nor carbon was satifffactory, the latter because of its reducing action. The necessary heat was produced by three Houck burners (Figure 1) supplied with fuel oil a t 80 pounds pressure and with air a t 1 pound pressure. It is essential that the burners be placed high enough above the melt so that the gases do not impinge upon the melt or else impurities are found in the product (caused by reduction of the barium sulfate). The furnace atmosphere must be oxidizing. It was found necessary to pass the exit gases through a water spray before sending them up the stack (Figure 2) as the salt vapors produce a bad fog in the neighborhood. 1981
1982
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Yol. 40, No. 10
This decolorizing material consisted of a mixture of 99.9% sodium chloride and 0.1% commercial superphosphate fertilizer, blown over the surface of the melt just before it left the furnace. The melt was quenched into a tank of water, air agitakd. It was pumped from this tank as a slurry; mashed in a thickener; filter pressed and dried in tray dryers; disintegrated to break up lumps; and bagged. The pilot plant produced an average of 50 tons of barium sulfate a day.
*/UL
PREPARATION OF WAR MATERIA
*“#“EN
Figure 1. Plan View of Furnace
AS salt goes through a plastic stage, the salt-barytes mix could not be introduced through a rotary kiln type waste heat preheater. Instead it was found necessary to blow the sabt-barytes mixture into the furnace (Figure 2) from a screw feed device, C, by a compressed air jet a t right angles to the flame jets. The particles melted and settled as rain in the furnace to form a molten pool without forming a crust.
It mas found necessary to dry both the salt and the barytes before using to prevent formation of hydrogen chloride by hydrolysis in the furnace. The mixture of dried salt and barytes in the proport,ion of 125 pounds of sodium chloride and 100 pounds of barytes were ground t,o 16-mesh7thus simult,aneeusly ensuring thorough mixing before feeding to the furnace through thenozzle, C. PROPERTIES OF PRODUCT
The barium sulfate produced by this process is a brilliant bluewhite material of an apparent gravity about one half that) of the precipitated product. A barrel that would hold 400 pounds of precipitated barium sulfate only holds 200 pounds of t,he barium sulfat,e from the saltprocess; this would correspond to an apparent specific gravity of 2.26. The product) likewise contained no free sulfur or sulfides and was found to be ideal for x-ray medical use. PRODUCTION C O S T S
The barytes used was shipped from Kingsport, Tenn., and the salt from nearby Cleveland, Ohio. The barytes used contains about 4oj, impurities and is available at low cost because of its unsuiiability for use in the regulax black ash furnaces. Figure 2.
Vertical Side Section of Furnace
The impurities, save for a trace of iron oxide, settled to the bottom and resembled a pool of viscous molten black glass. This was removed periodically by tipping the furnace forward by the elevator, E, and raking out the residue through the cleanout hole, D. This residue amounted t o 80 pounds per ton of barytes. The baffle, A , prevented the residue from moving forward v,ith the melt, and baffle H stopped air-injected particles of ore from falling into the decantate pool, P. Baffle B prevented floating impurities from contaminating the product and formed a quiet chamber into which the material for decolorizing the trace of impurities in the melt could be blon-n through the screw feed, F . Figure 3.
TABLEI. PRODUCTION COSTS-BLANCFixx
Barytes per ton (2000 pounds) f.0.h. Willoughby, Clhin
lO%--;-dditional Salt, per ton f.0.b. Willoughhy, Ohio Oil, 100 gal. a t S0.0625/gal. Steam Bags La5or Water, power, light, oils, andincidentals Cost for 1920 lb. Cost per ton
FROM
Pilot Plant Sl2,OO 1.50
8.85 6.25 1.oo 2.00
16.50 3.00 S54.10 $56,34
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Cross Section of Furnace
BARYTES
Estimated for Large Plant Operations $15.00
I n Table I the pilot plant figures were taken from actual practice. The estimated figures for large plant operation are liberal and probably could be reduced in most locations.
1.20 1.70
3 .OO 1.00 2 no 12.00
__ 3.00
$39.20 840. a2
LITERATURE CITED
(1) Booth, Harold S.,U. S.Patent 2,013,401 (Sept. 3, 1935). (2) Moffatt, A, British Patent 22,033 (Sept. 22, 1910). (3)
Rentschler, M. J., U. S. Patent 1,959,305(May 15,1934).
RBCEIVEDApril 10, 1948,
