Chapter 32 National Metallurgical Laboratory (Madras Centre) Council of Scientific and Industrial Research Taramani, Madras -600113, India. Abstract. Three types of flotation columns were developed with a column dia of 8.0 cm and a length of 160cm. The first type consists of an ordinary column fitted with a porous plate at the bottom. The second type consists of two electrodes at the bottom to obtain very fine and uniform bubbles generated electro- lytically and the third is a combination of first and second types, i.e. to get both ele- ctrolytic bubbles and air from the compressor through porous plate. Three different ores were tested-gold tailings for recovery of scheelite, copper tailings (chalcopyrite) and oxide copper ore. In the case of scheelite and copper oxides, good results were obtained with the first type of column itself, whereas thethird type column was found fairly effective in the recovery of chalcopyri te. The variables like the effect of reagent concentration, column height above the feed point, feed flm~ rate, current density, air flow rate, particle size etc. were examined. In recent years the subject of column flota- tion has gained much importance in mineral pro- cessing research and development. Column flo- tationhas been claimed to give better separa- tion than conventional flotation cells particu- larly on fine materials. It was proposed to test the response of some tailings carrying low mineral values, finely disseminated, to the treatment in flotation columns developed in the laboratory. Onecase of oxide copper ore was also proposed for examination with the flotation column. An attempt has been made to recover chalco- pyrite from flotation tailings of the plant of Hindusthan CopperLimited, (H.C.L.), Rakha, Bihar, India. In this plantapproximately 700 tons per year copper is lost in the tailings \~ith the ore treatment plant capacity at 1.55 million tons per year. This works out to be around 5% of the total copper production at the above plant. The copper minerals in the tailings were found to be either interlocked with the gangue or in slimes. Similarly, considerable amounts of tungsten in the form of scheelite is let out in the tailings of gold ore from Kolar Gold Fields, Karnataka, India, without processing. Usual gravity concentration methods tried earlier were found not attractive in achieving good recovery of scheelite. Another oretried in this investigation is a mixture of copper oxides where malachite and azurite are predominant. Over 5.5 million tons of copper oxide ore at Malanjkhand copper mine of Hindusthan Copper Limited, India, is presently stock piled in theabsence of a suitable benefi- ciation process. The gradual depletion of high grade mineral deposits and the need of mineral conservation has turned the attention of mineral industries to develop alternate beneficiation procedures to recover the values from the low grade finely disseminated ores. Three different ores shown inTable I were taken up for theinvestigation. Sodium diethyl dithio carbamate (DTC) and potassium ethyl xan- thate (KEtX) both Analar Grade were used as collectors for copper minerals. Purified Naphthe- nic Acid and Oleic Acid were used as collectors for scheelite. O.lN SodiumSulphate (AR grade) was used as an electrolyte in electroflotation experiments. Flotation column Three types of perspex flo- tation columns were fabricated with a column dia of 8.0 cm and a length of 160 cm. The first type was of an ordinary column fitted with a porous plate at the bottom (Fig.l, Type I). The second type consisted of two electrodes at the bottom (Fig.l, Type II) to obtain very fine and uniform bubbles generated electrolytically. Thisarrangement is similar to that of simple elec troflotation cell. Nickel coa ted stainless
Transcript
Chapter 32
National Metallurgical Laboratory (Madras Centre)Council of Scientific and Industrial Research
Taramani, Madras - 600113, India.
Abstract. Three types of flotation columnswere developed with a column dia of 8.0 cm anda length of 160 cm. The first type consistsof an ordinary column fitted with a porous plateat the bottom. The second type consists oftwo electrodes at the bottom to obtain veryfine and uniform bubbles generated electro-lytically and the third is a combination offirst and second types, i.e. to get both ele-ctrolytic bubbles and air from the compressorthrough porous plate. Three different oreswere tested-gold tailings for recovery ofscheelite, copper tailings (chalcopyrite) andoxide copper ore. In the case of scheeliteand copper oxides, good results were obtainedwith the first type of column itself, whereasthe third type column was found fairly effectivein the recovery of chalcopyri te. The variableslike the effect of reagent concentration, columnheight above the feed point, feed flm~ ra te,current density, air flow rate, particle sizeetc. were examined.
In recent years the subject of column flota-tion has gained much importance in mineral pro-cessing research and development. Column flo-tation has been claimed to give better separa-tion than conventional flotation cells particu-larly on fine materials.
It was proposed to test the response of sometailings carrying low mineral values, finelydisseminated, to the treatment in flotationcolumns developed in the laboratory. One caseof oxide copper ore was also proposed forexamination with the flotation column.
An attempt has been made to recover chalco-pyrite from flotation tailings of the plantof Hindusthan Copper Limited, (H.C.L.), Rakha,Bihar, India. In this plant approximately 700tons per year copper is lost in the tailings\~ith the ore treatment plant capacity at 1.55million tons per year. This works out to bearound 5% of the total copper production atthe above plant. The copper minerals in the
tailings were found to be either interlockedwith the gangue or in slimes.
Similarly, considerable amounts of tungstenin the form of scheelite is let out in thetailings of gold ore from Kolar Gold Fields,Karnataka, India, without processing. Usualgravity concentration methods tried earlier werefound not attractive in achieving good recoveryof scheelite.
Another ore tried in this investigation isa mixture of copper oxides where malachite andazurite are predominant. Over 5.5 million tonsof copper oxide ore at Malanjkhand copper mineof Hindusthan Copper Limited, India, is presentlystock piled in the absence of a suitable benefi-ciation process.
The gradual depletion of high grade mineraldeposits and the need of mineral conservationhas turned the attention of mineral industriesto develop alternate beneficiation proceduresto recover the values from the low grade finelydisseminated ores.
Three different ores shown in Table I weretaken up for the investigation. Sodium diethyldithio carbamate (DTC) and potassium ethyl xan-thate (KEtX) both Analar Grade were used ascollectors for copper minerals. Purified Naphthe-nic Acid and Oleic Acid were used as collectorsfor scheelite. O.lN Sodium Sulphate (AR grade)was used as an electrolyte in electroflotationexperiments.
Flotation column Three types of perspex flo-tation columns were fabricated with a columndia of 8.0 cm and a length of 160 cm. The firsttype was of an ordinary column fitted with aporous plate at the bottom (Fig.l, Type I).The second type consisted of two electrodes atthe bottom (Fig.l, Type II) to obtain very fineand uniform bubbles generated electrolytically.This arrangement is similar to that of simpleelec troflotation cell. Nickel coa ted stainless
steel gauze and copper gauze were used as anodeand cathode respectively. Both the electrodesware arranged horizontally just one above theother. Maximum care was taken in the alignmentand the gap between the electrodes to minimisepower loss and at the same time to avoid anyshort circuiting of electrodes. The third typeof flotation column (Fig.l,Type III) was a combi-nation of first and second types, i.e. to getboth electrolytic bubbles and air from thecompressor through porous plate. Sintered platewith G-4 poracity cut to 6.5 cm dia and fittedin a funnel was used as a diffuser element.A ratio of 0.8 for the diameter of air diffuserto column was maintained which was recommendedas optimum by Narasimhan et.al (1972).
--~--FIGURE 1 : Schematic diagrams of
different flotation columns
Constant wash water flow of 1.0 l/min wasmaintained throughout the experiments from thewash water spray arrangement, which was arrangedjust above the column to clean the entrainedgangue minerals. Provision was made to collectthe froth and tailings.
All the experiments were conducted as singlestage operations. In each experiment 2 kg ofmaterial was conditioned with the depressant,collector and frother in the conditioning tankand pumped through a slurry pump connec ted tothe feed point of the column. Pulp density 20%solids was maintained in the conditioning tank.Pine oil was used as a frother in the case ofcopper minerals, whereas no frother was added ~in the flotation of scheelite.
Estimation of copper in the froth and tailingswas done in an Atomic Absorption Spectrophoto-meter (AA 575 Varian Techtron) and that of tung-sten by U.V.-Visible spectrophotometer colori-metrically (Young, 1971).
The chemical and sieve analysis of the coppertailings as received are indicated in Table II.
The analysis of the tailings indicates that 50%of the copper ores present in the finer fraction,i.e. below 75 microns and around 30% in coarserfraction (above 150 microns). Copper lost inthe tailings is mostly due to the incompleteliberation of copper mineral and slime coating.An attempt was made to refloat this tailingsin a Denver Sub Lab Flotation Cell using KEtXand DTC as collectors. Though the recovery(25.7%) was low, the grade 2.4% copper usingDTC as collector was comparatively better thanthat of KEtX as a collector where recovery andgrade are 27.1% and 0.87% respectively. Basedon the better selectivity of DTC as collector,it was decided to carry out the further experi-ments using DTC as collector.
From the liberation analysis it was found thatchalcopyrite grains are fully liberated below75 microns. So copper tailings ground to -75microns were used as feed to the column flotationexperiments. The material was conditioned with3 Kg per ton of sodium silicate for 10 minutes,
followed by the addition of 0.5 kg per ton ofpine oil for 5.0 minutes.
Initially, come column flotation experimentswere conducted to find out the optimum dosageof collector. Results of the same are shownin Fig. 2. From the figure it could be seen that
the optimum collector concentration for copperoxide and chalcopyrite tailings are 1.5 kg perton and 0.6 kg per ton respectively. It maybe noted that the concentrations are not higherthan those experienced in conventional flotation.
The results of the column flotation experimentsconducted on copper tailings and copper oxideores at different air flow rates are shown inFig. 3. It is observed that the recovery increa-sed with the air rate upto a point and there-after gradually decreased. Both the grade andrecovery were found to be optimum at 7.5 l/minof air flow. Also it could be seen that airflow rate has significant effect on the enrich-ment ratio of the mineral. Back mixing and turbu-lance was noticed at higher air flow rates.
Fig. 4 shows the effect of feed (slurry) flowrate on the recovery and enrichment ratio ofcopper tailings and oxide copper ores. Itwasobserved that as the feed flow increases, theenrichment ratio decreases with no significantchange on the recovery of values. It may bedue to the effective washing of the froth atminimum feed rate.
60 r--I " I/J
T I_---.~TA'" '"I I \ "... - -~.1
-o! 40 \ ~ ~~ \ 0
\ t=
~~\, a:~a: , z
i....'a.~Z> UJ::I
:I:20 Sd0 a:u z
UJ10
FIGURE 3height 80DTC 1.50.6 kg/ton
,.I 60II...!.
>a:~ 40ouUJa:a:~& 20u
5 10AIR FLOW I / min
Effect of air flow.cm above feed point,kg/ ton of copper oxidefor copper tailings (.).
ColumnReagent
(0) and
109=ca:
0.1., 0.6 0.8FEED ( SLURRY) FLOW I / min
FIGURE 4 Effect of feed flow. Columnheight 80 cm above feed point, Air flow7.5 l/min, Reagent DTC 1.5 kg/ton forcopper oxide(oJ and 0.6 kg/ton for coppertailings (. ) .
The effect of column height above the feedpoint on the recovery and enrichment ratio forcopper tailings and copper oxide ores is shownin Fig. 5. For 8.0 cm dia column a height of80 cm on either side is considered significantto give optimum performance.
60 30I
~--~-.•...•.. I
'I ",¥ /"" II .•.. ",
II '" II ....KI 40 .•...... I
20-- I~ I,> ~ ____ ....0- ___ -,c" ~a:UJ
...> <8 a:
~...
20z
10 UJa: ~UJ :I:11.ll. U
0 a:u z
UJ
20 40 60 80COLUMN HEIGHT, Cm (ABOVE FEED POINT)
FIGURE 5 Effect of column height abovefeed point. Air flow : 7.5 l/min, Feedflow: 0.6 l/min, Reagent DTC : 1.5 kg/tonfor copper oxidelO), 0.6 kg/ton for coppertailingsCe). ,
However, from the above results it is clearthat the recovery and the enrichment ratio ofcopper concentrate from both the samples isnot so attractive. The same copper oxide arebeneficiated earlier by conventional flotationmethod has yielded excellent results with anoverall recovery of 90% and a grade of 35% copper(Prabhakar et .al 1988). Though the grade wasslightly better, the recovery was poor withcolumn flotation (Figs. 2 - 5). Hence furtherexperiments were planned to probe the causeof the low recovery. A set of experiments wereconducted with various particle sizes and theresults are shown in Table III. From the resultsit is apparent that the column flotation tech-nique is most efficient for the beneficiationof intermediate size fraction, i.e. -75+45 mic-rons. The low recovery of coarse fraction maybe the reason for the overall low recovery statedabove. However there appears to be a drasticdeterioration in the grade with the finer frac-tion, but with appreciably higher recovery.
We wish to consider the prolem of poor reco-very and grade from copper tailings sta ted ear-lier. Based on the earlier experience on thebeneficiation of chalcopyrite fines by electro-
Flotation of various sieve fractions of copperoxide are with its wt.% in head sample
flotation (Bhaskar Raju and Khangaonkar 1982,1984), it was assumed that introducing finebubbles .generated electrolytically in the columnmay help in obtaining better results. Hencesome experiments were conduc ted using elec tro-lytical bubbles in the flotation column typeII. The results shown in Table IV have revealed
Results with electro-column (Type II)on copper tailings
that there is no improvement both in recoveryand grade. However. experiments conducted ina combined column type III have shown (TableV) some improvement both in recovery (68%) and
Results with combined column (Type III)on copper tailings
grade (2.4%). However these results are inferiorcompared to those in a simple electroflotationapparatus (Bhaskar Raju and Khangaonkar, 1986).The results for poor metallurgy in column flota-tion using electrolytic bubbles are complex.Thorough analysis of the hydrodynamics may helpin understanding the reasons.
Separate set of experiments were conductedto beneficiate scheelite from gold tailings.Since the column flotation is effective below75 microns, the material was ground to below75 microns and used as a feed in column flotationexperiments, using column flotation unit TypeI. The ground tailings were conditioned with0.5 kg/ton of lime followed by 2 kg/ton of sodiumcarbonate and 3.6 kg/ton of sodium silicatewith a conditioning time of 10 min after eachaddition. These values are found to be optimumin preliminary experiments. Oleic acid, naph-thenic acid and the combination of both weretried as collec tors. 10 min conditioning wasmaintained after the addition of collector.1:1 (by weight) Naphthenic acid and oleic acidwas found to be very effective collecting systemin the presence of above conditions.
During the experiments, it was observed thatunslimed ore yielded only 68.2% recovery andan enrichment ratio of 16. Desliming enabledmuch better recovery (95%) and an enrichmentof 50. Hence all experiments regarding thestudy of air flow, slurry flow, etc. were con-duc ted on des limed ore. The results are shownin Tables VI to IX. The optimum conditions were
Effect of collector (1:1 Naphthenicacid 'and Oleic acid)
Air flow: 7.5 l/minFeed flow: 0.6 l/min
80 cm above feed point.
Collectorkg/ton
Enrichmentratio
% W03
Recovery
0.040.080.120.160.20
42.351.452.845.739.9
73.588.791.392.190.2
observed to be air flow 7.5 l/min, slurryflow 0.6 l/min., column height 80 cm above feedpoint and collector 0.08 kg/ton of 1:1 Naphthenicacid and Oleic acid.
A test was conducted for the above scheelitedeslimed sample in a conventional Denver LabFlotation Cell, with the reagent conditionssame as above. The recovery was 95% and enrich-ment ratio was 15.5. It is therefore apparentthat column flotation has given a much bettergrade.
1. For the samples of copper tailings, oxidecopper ore and gold tailings (for scheelite),it was observed that column flotation yieldedbetter enrichment ratio.
2. It was observed that feed (slurry) flow andair flow have significant effect on the bene-ficiation of ores in column flotation.
3. For the abovewas found to be-75+45 microns.
materials, column flotationmore effective in the range
Bhaskar Raju, G., and Khangaonkar, P.R.,"Electroflotation of Chalcopyrite Fines"J. Min. Process., Vol. 9, 133 - 143.
1982Int.
Bhaskar Raju, G. and Khangaonkar, P.R., 1984."Electroflotation of Chalcopyrite Fines withSodium diethyl dithiocarbamate as Collector"Int. J. Min. Process., Vol. 13, 211 221.
Bhaskar Raj u, G., and Khangaonkar, P . R., 1986."Studies on the Beneficiation of ChalcopyriteTailings - A New Approach". Paper presentedin the National Seminar on Fine Particle Pro-cessing, Dhanbad, India.
Narasimhan, K. S. ,1972. "ColumnRecovery". Eng.84 - 85.
Rao, S. B. and Choudhury, G. S. ,Flotations Improves GraphiteMining J., Vol. 173, No.5,
Prabhakar, S., Bhaskar Raju, G. and KhangaonkarP.R., 1988. "Studies on the Beneficiationof Copper Oxide Minerals". To be presentedin XVI Int. Min. Pro. Cong., Stockholm, Sweden.
Young, R.S., 1971. "Chemical Analysis of Extra-ctive Metallurgy". Charles Griffin-London,346 - 353.
