. HEAVY MINERALStONCENTRATION AND GLASS-GRADE. SILICA PRODUCTION BY FROTH FLOTATIO~

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1 . '. I 74-VIII-P. HEAVY MINERALStONCENTRATION AND GLASS-GRADE. SILICA PRODUCTION BY FROTH FLOTATIO by Robert M. Lewis Mineral Dressing Engineer MINERALS RESEARCH LABORATORY NORTH CAROLINA STATE UNlVERSITY 180 Coxe Avenue Asheville, North Carolina 28801

2 i ' ABSTRACT Extensive exploration is being undertaken to locate silica ore deposits from which high quality silica sand can be produced for the flat glass industry. Silica sand deposits are usually contaminated with various heavy minerals which are detrimental to flat glass making and therefore must be removed to make the silica useful. Specifications call for a product essentially not coarser than 40 mesh, nor finer than 140 mesh. The maximum total iron is limited to 0.080% Fe203 with an acceptable variance of 0.040% maximum. Refractory minerals such as zircon, kyanite, sillimanite. chromite, corundum, and andalusite are limited to grams of plus 70 mesh refractory minerals per 100 pounds of sand; this calculates to be % by weight, or 4.4 parts per million. Known flotation procedures were tried at the North Carolina State University Minerals Research laboratory to remove contaminant minerals from silica ores. These procedures gave marginal products, and were either too sensitive or too costly for efficient operation. A State-supported research project was undertaken by the Minerals Research laboratory to develop an efficient and economical procedure for producing flat-glass-grade silica by froth flotation. This was accomplished in batch tests and verified through pilot plant operations. Silica products assaying 0.03% Fe203' and containing a limited amount of refractory minerals, were produced by the new flotation procedure.

3 pc h 't 0"3 0 rttrt etc, INTRODUCTION Considerable interest has been 'shown by several companies in establishing mining operat1ons in North Carolina and neighboring states for the production of flat-glass-grade silica products. This has been brought about by the construction of several plants for production of glass products, including one of the world's largest flat-glass plants. Several companies solicited the services of the Minerals Research Laboratory for batch testing of sand samples using known procedures. Pilot plant operations were performed on ores from different areas in the State and from neighboring states. These resulted in flowsheets which produced satisfactory glass-grade silica, but the processes appeared to be excessively complicated; therefore, a Statesupported project was undertaken to develop a flotation procedure for more efficient and economical removal of heavy mineral contaminants from silica ores. The ultimate objective of this research was the production of glass-grade silica from close proximity to North Carolina glass plants. An efficient and economical flotation procedure was developed and found to be effective when tested by batch tests and pilot plant tests on samples from various deposits. PROCEDURE The primary feature of this procedure is the use of detergenttype reagents, such as a sodium alcohol ether sulfate (Tex-Wet 1158) and a dodecy1benzene sulfonic acid (Tex-Wet 1197), as heavy minerals collectors in an acid circuit for froth flotation. These reagents were

4 - 4 - obtained from Intex Products, Inc., Greenville, South Carolina; however, other brands of like chemicals were found to be satisfactory. The sodium alcohol ether sulfate-dodecyl benzene sulfonic acid collector adheres to the heavy minerals rendering them hydrophobic, thereby allowing attachment of air bubbles and removal of the heavy minerals as a froth product. Silica remains in the chamber, not being affected by the collector and being suppressed by the acid media at low ph. Reagents for froth control, such as pine oil, methylisobutylcarbinol, and fuel oil, were found not to be necessary for removal of heavy mineral contaminants as a froth product. BATCH TEST The ore for this test came from the Sand Hills area of North Carolina and contained approximately 0.50% heavy minerals, such as ilmenite. magnetite. zircon, kyanite, etc. A 500-gram sample was rod milled for three minutes at 25% solids. The material was then screened on 28 mesh, and the oversize placed in an oven and dried. The undersized material (minus 28 mesh) was placed in a bucket and water added to create a thi slurry. The slimy water was rejected as a through product on a 150 mesh screen. The minus 28 plus 150 mesh material was attrition scrubbed at high solids (75%) for ten minutes with 2.0 pounds of 66 0 Baume H 2 S0 4 per ton of ore (added as a 2% acid solution). The material was then des1imed as done previously. The deslimed ore was then placed in a beaker to which was added 1.0 pound of reagents blend (50% sodium alcohol ether and 50%

5 _ -... ' dodecylbenzene sulfonic acid) per ton of head feed. The material was conditioned for ten minutes at 65% solids. The material was then transferred to a flotation cell and water added to the cell. The contents were conditioned for one minute in the cell after which the air was turned on causing levitation of the heavy minerals and subsequent removal as a froth product. The material remaining in the cell constituted the solica product. All process samples were dried, weighed, and a material balance determined. Samples were subjected to heavy liquid (Sp. G. 2.96) separation for control. The test described above produced a silica product assaying 0.004% heavy minerals. The plus 70 mesh fraction of this product contained less refractory minerals than the limited amount specified for sand used as a raw material for most glasses. Eighty-three percent of the ore was recovered as a product, with 10.1% being wasted as slimes and 6.7% going to tailings. PILOT PLANT TEST The ore for this test came from the Sand Hills area of North Carolina and the same general area as that of the material used in batch tests. The ore contained approximately 0.50% heavy minerals, such as ilmenite, magnetite, zircon, kyanite. etc. Ore was loaded into a hopper and fed with a belt conveyor at 200 pounds per hour to a rod mill. The are was ground at 60% solids density for a retention time of 33 minutes. The mill discharge gravitated to a stationary screen for removal of trash. The screen undersize material was contained in a sump and pumped to a cyclone for

6 - 6 - desliming. The cyclone underflow material.gravitated to a spiral classifier for additional slime removal and dewatering preparatory to attrition scrubbing. The high density material from the classifier was attrition scrubbed at 70 to 75% solids for 35 minutes in a pulp containing 2.0 pounds of 66 0 Baume H2S04 per ton of ore (added as a 2% acid solution). The scrubber discharge material was pumped to a cyclone for desliming. The cyclone underflow material gravitated to a spiral classifier for additional slime removal and dewatering preparatory to conditioning. The discharge from the classifier was conditioned for 34 minutes at 61% solids density in a pulp containing 1.0 pound per ton of feed of a half and half blend of sodium alcohol ether sulfate and dodecylbenzene sulfonic acid. The conditioned material gravitated to the flotation cells, where the contaminant minerals were removed as a froth product and the silica product recovered in the machine underflow discharge. Eighty-two percent of the ore was recovered as a product, with 10.0% being wasted as slimes, and 8.0% going to tailings. The product assayed % heavy minerals, and 0.028% Fe203' The plus 70 mesh refractory minerals reported as parts per million of total sample were: 2.2 kyanite and 4.4 zircon. The process variables in the pilot plant coincided with those in the batch test with the exception of retention times. Additional retention time was maintained in the pilot plant due to equipment sizing. Pilot plant tests were conducted in which the collector reagents were recirculated. The reagent consumption was reduced from 1.0 to 0.2 pound per ton of are.

7 - 7 - CONCLUSIONS There are several advantages of the flotation procedure described over standard procedures now employed: 1) The float is more effective, in that it rejects approximately 100% of the heavy minerals; 2) The float is very selective and has a good quiescent zone. with little carry-over of fine sands into the heavy mineral froth producti 3) Reagent costs are the same, or less, than those of current commercial procedures; 4) The collector reagent is biodegradable, giving it a big advantage in pollution control.

8 _ PILOT PLANT FLOWSHEET Denver 1211 X 7' Denver 1211 X 2411 are (200 lbs/hr) Be 1 t Conveyor Wa ter added -----:. t " Opening Water added Denver 1" Vertic1e Dorr 3 11 Rod Mill Trash Screen ! 1 C:i.ct one :,.,. +" Trash Denver 12" X g' H 2 S0 4 added Wemco 6-Pot Water added Denver 111 Verticle Dorr3" Screw Classifier i Attrition Scrubber ----! f C:i.Cio ne -140 Mesh Slime Denver gil X gil Reagents added 2-Pot ; Screw Classifier Conditioner Water added I Ga1igher Agitair 4-cell Flotation Cells 1 Sil ica Product ,..,.".. Heavy Minerals Ta; 1 ; ngs

9 - 9 - SCREEN ANALYSES "t:i C... ttl 60 s::: U 50 S > 40 ttl po- 30 E U Inches -- - a I Pan '- U. S. Mesh A B C SCREEN SCALE RATIO L-O-F Specs. Pil,t Batch Test Plant rest Openinss Per Cent Per Cent Per Cent ; Per Cent Tyler U.S. MIIII- Per Cent Cumulative Por Cent Cumulative Per Cent Cumulative: Per Cent Mesh No. Cumulative meters Weillhts Welshts Welshls I Welsh!s I , I I i I.0232.S I 0.0 i:: I 'l.O 2 0 I i 64.5 bl I l- Q-.-Q-!, f:)_ 9: I 2.1i.3:.;j 93.4 I I I ' o.o.: L ;_ J lorrn-.!l.oo. 0 1 ==J-----=- _.1 -To13Is.1 i I I I Pan I' _ I t J ---- i. L, !-, _ I I