US2136341A - Flotation of culm - Google Patents

Description

" disposing of the slush culm which is usually Patented 8,

'PATENTOFFICE' FLOTATIONOF CULM Norman Hadley, Westfield, N. J., aaim'r to "American Cyanamid Company, N. Y., a corporation of Maine,

N ew York,

a. Drawing. Application- September 1, 1936, v 1 Serial No. 98,975 4 Claims. (or. 209-166) This invention relates to the flotation of. slush culm and other refuse coal. In .a more specific modification, the invention is especially concerned withthe recovery of 'low ash coal from anthracite:

- slush culm or other anthracite refuse.

"The problem of coal refuse, both bituminous and anthracite, has long been a serious one in the industry. The refuse coal is mainly contaminated with high ash material and is not useable as such. As a esult, serious losses of good coal: in flnesizes ares'ufiered by the industry, and they have to incur considerable expense in pumped into large culm banks. Many-mines do not have sufli'cient fairly level ground for culm banks. and when the banks are placed on too great a slope, rain washes thecoal into the rivers and a seriousnuisance. frequently arises. Slush culm banks, particularly bituminous coal, also tendto ignite and burn for years with serious annoyance from smoke and fumes. represented by the good coal in the culm or'other refuse are, of course, much more serious'in the anthracite industry than in the bituminous inin the breaker and I dustry, because the unit value of anthracite coal is higher than bituminous and the character of the anthracite coal results in greater degradation hence larger proportions of the slush culm.

Flotation of .coal refuse has been proposed and has been used fairly extensively in Europe prithat bituminous coal represents asomewhat easier flotation problem.

When refuse coal is floated. such as anthracite slush culm, and in the following more specific discussion of the invention the description will/be based on the purification of anthracite slush culm although it should be understood that the features are also applicable to .bituminous coal, the

culm contains a mixture of materials varying both in size and in composition. That is to say, there is a certain amount of coal, for example about 60% in representative anthracite culms, which is very low in ash, containing less than 10% of ash and approaching the actual inherent coal ash for coalfrom that particular area. This good coal occurs in a wide range of sizes running from down to very fine particles less than 100 mesh (Tyler Standard Series). The accompany+ ing 40% of higher ash material, of course, grades c contaminated by any considerable portions of frommaterial with only slightly higher ash than also occurs in practically The losses lern even more difficult.

the good coal, down to material which is mostly ash with only little coal.

as the good coal. v

The flotation ofcoal, using standard flotation reagents which are for the most'part hydrocarbons such as kerosene accompanied, if necessary, by suitable frothers, is based on wettability of the coal by the oil and the'coal therefore tends to attach itselfto the froth bubbles and appears in the concentrate. Since, however, the material coal (having only inherent ash) to a slaty gangue impregnated with small amounts of coal, it is diflicult and has hitherto been impossible to oh- This high ash material as wide a range of sizepresent in the culm grades all the way from pure tain a sharp flotation separation with good re-' covery such as is commonly found in the flotation of 'sulflde minerals and free gold because the good coal is not'entlrely liberated from the gangue. The problem might be considered as one in which it was necessary to float a concentrate of mineral values away from a partlymineralized J gangue. Due to the fact that the coal to be recovered forms a large propcrtion of the feed.

usually somewhat over half, avery large bulk of onthe flotation machines and renders the. prob- The goal of a flotation cleaned coal from anthracite culm is less than 10% ash. It has been proposed to, fioatslush culm by grinding down to a uniform fine size. These proposals are without economic value as the grinding plant is as large as the flotation plant and the result of grinding reduces the value of the clean coal obtained.

Previous attempts to clean anthraciteslush culm followed the general flotation procedure which has been used withslight success on bituminous concentrate which contains a large portion of the good coal, say from 80% up, but such a concentrate is not low in ash and cannot be economically cleaned. Attempts to improve the grade of thecoal ooncentrateby reducing the amount of reagents used'were also unsuccessful. It was possible toobtain a concentrate of the des red ash content but only at the expense of very serious losses in recovery. All attempts to vary flotation procedure failed to produce both good recovery and a lowash concentrate.

.The presentinvention is based on the discovery' that it is possible to floata full size range of refuse coalsuch as anthracite slush culm, with a very'small. amount of-reagents so that classified preferably by screening and the fine iii material which consists almost exclusively of fine high ash material, is rejected. The coarser material, while it contains all of the coarse low ash coal, is still contaminated with a certain amount of coarse high ash material, and therefore screening of\ the tailings will not recover the coarse coal in the form of a sufliciently low ash material. However, the oversize from the classification of the tailings can then be floated under conditions which will result in the flotation of coarse low ash coal particles and diniculties will not be encountered because the high ash material is all likewise coarse and therefore does not float oil into the concentrate and the problem of contamination with high ash material is solved.

The present invention not only results in obtaining 25. better recovery of low ash material, but also results in an increased capacity of flotation equipment. The consumption of collector which is usually kerosene or a similar .hydrocarbon, is aiso ,decreased. I

It is an advantage of the present invention that the standard reagents can be used. However, it has been found that a frother consisting of paraflin alcohols of 7 to carbon atoms stabilized with a hydrocarbon gives better results and in a more specific aspect the invention includes this feature.

While the invention may be used with any type I of flotation machine, best results are obtained with mechanical machines.

are well suited for floating the. wide range of sizes -which is necessary in carrying out the present invention.

The process of the invention is very flexible and is well adapted to handle refuse coal of difl'erent types to produce products for various markets. Thus, forexample, in many cases there is a good market at a higher price for coarser coal sizes and it is desirable to keep the fine rougher concentrate separate from the floated coarse portion of the tailings. In other cases, for example where the clean coal .is to be pulverized, it may be desirable to mix the two final products together.

Where the ash requirements are not unduly severe, therougher concentrate may remain uncleaned-but where the minimum ash is required, it is desirable ,to clean the rougher concentrate as such aycleaning operation will greatly reduce the ash without material loss in good coal. Of coarse, the additional cleaning operation of the rougher concentrate necessitates additional flotation equipment .and slightly increases the amount of reagents. The particular compromise best suited for any given condition is largely determined by economic considerations and it is an advantage of the present invention that it is flexible and that the best and most profltabl compromise can be chosen.

The invention will be described in greater ae-v areas-i1 tail in conjunction with the cleaning of anthracite slush culm from the bank orl current production of the Philadelphia 8; Reading Coal it Iron, Company. it should be understood that the exact details of flotation type, reagent consumption, and the like, will vary somewhat with difierent culm and with different coals, and the invention is therefore in no sense limited to the precise details of the specific examples.

Example 1 Slush culm from the Locust-Summit Breaker of the Philadelphia in Reading Coal a Iron Company was floated in standard Fagergren flotation machines with .276 lb. per ton of a frother consisting of a mixture of paraffin alcohols or" 7 to 10 carbon atoms and stabilized With a hydrocarbon, and which is described in the patent of Christmann and Jayne No. 2,065,053 issued December 22, 1936, without any hydrocarbon collector. A concentrate was obtained which contained fine coal only, then the tails were classifled in the presence of 0.5 lb. per tonof sodium silicate and after rejection of the finer material5 lbs. per ton of kerosene were added to the residual pump at about 50% solids and the pulp then diluted to solids and floated in a second set of flotation machines.

The original culm had an ash content of -26%, and the results obtained by the treatment are summarized in the following table:

Cumulative Weight, Ash,

Product percent percent Weight Ash,

percent percent Gone 1 23.55 121 26.56 12.1 Gone. 44. 14 11.0 70. 70 11. 4 Tail 1e. 55 56. 0 s7. 25 1o. 9 Rejected fines Ta 75 622 100.00 25.3

Example 2 High ash 51am culm from the Locust-Summit Breaker of the Philadelphia & Reading Coal 8:

Iron Company having approximately 40% ash, was floated at 21% solids in standard Fagergren flotation machines with .0322 lb. per ton of the frother described in Example 1. A rougher concentrate is obtained which contains the fine low ash coal. The remaining pulp is then screened at 28 meshand .092 lb. per ton of frother and 4 lbs. per ton of kerosene added to the"+28 mesh material. This coarse material is floated to give a second rougher concentrate, and both rougher concentrates are cleaned using .092 lb. per ton of additional frother in each case. The results obtained are shown in the following table:

In'the claims the term coal of frotmflotation size" is intended to cover coal of a size passing through 10 mesh screens and'has no-other mean-- l ing. This represents about the coarsest coai which can be floated by a froth flotation process.

What I claim is:

1. A method of cleaning refuse coal which comprises subjecting therefuse coal of froth flotation size to'a froth flotation process with an 1 amount of reagent insufllcient to float flne high ash particles whereby a concentrate is produced containing a major portion of flne low. ash coal particles, classifying the flotation tailings, rejecting the fine sizes and subjecting the coarse particles. I r

2. A method of cleaning anthracite slush culm culm of mm flotation size to a froth flotation process with anamount of reagent insufllcient to float fine high ash particles whereby a con v cen'trate is produced containing a major portion oi flne low-ash coal particles, classifying the flotation tailings, rejecting the fine sizes and subjecting the coarse sizes to froth flotation with an s. A method according to claim 2 in which'the tailing is sized on a screen at approximately 28 which comprises the anthracite noam nsnmr,

' amount of-fiotation reagent suflicient to float coarse low ash particles.