Indian Journal of Chemical Technology Vol. 6, September 1999, pp 280-284

Flocculation of iron ore slimes from Joda and Kiriburu mines

Ram Pravesh Bhagat & Shobhana Dey

Mineral Processing Division, National Metallurgical Laboratory, Jamshedpur 831 007, India

Received 8 February 1999; accepted 13 August 1999

The present paper reports the flocculation of iron ore slimes from Joda mines of TISeO and Ki riburu mines of SAIL situated in the west Singhbhum district of Bihar, India. These two slimes had marginal difference in density. The presence of clay minerals was more in case of Joda slimes. The settling rate following flocculation was measured as function of time. The effect of pulp density and flocculant dose at neutral pH was studied in the tests. The sedimentation rate increases with increasing flocculant dose up to a certain limiting value after which the improvement is marginal. The pulp density and flocculant dose have considerable effect on the settling rate. Joda slimes has poorer settling characteristics in comparison with Kiriburu slimes. The effect of pulp density and minerals present in these slimes are apparent from these observations.

The processing of fine grained ores frequently results in the production of ultra fine particles, commonly called slimes. These account for a major material loses, particularly for iron ore in view of large tonnage treated in India or elsewhere in the world . Safe disposal of slimes followed by some subsequent treatment and recycl ing of water need solid - liquid separation. Besides, it has drawn considerable attention during the recent years because of the pollution of downstream water. Fine particles in a fluid suspension tend to follow the motion of the fluid rather than moving relative to it, under the influence of any external force applied to achieve a separation. The formation of larger units by aggregation is thus a promising way to overcome this hydrodynamic limitation . Water soluble starch and polyacrylamides with variolls ionicity have played a considerable role in solid water separation related to mineral processing industries and red mud treatment l

-3

. Efficient flocculants are now commercially available and find application as thickening and filtration aids.

Flocculation of mineral suspensions usmg polyacrylamides has been investigated by many authors4

-6

. Selectivity in flocculation using starch in case of minerals like hematite, calcite etc. has been reported in the literature7

-lo

. pH value of the suspension affects the settling in two ways:

• The surface charge of the particles changes with pH which affect inter particle attraction! repulsion.

• pH controls the degree of ionisation of the polymer and determines the degree of extension of the polymer molecules" .

The effect of pH on the settling rate of Joda s limes has been investigated in the past. It was observed that the settling rate decreases considerably in the alkaline suspension (PH 10) whereas there is marginal change in the settling rate when pH value changes from 6.4 to 5.0 12 .

The present paper reports studies on the flocculation of iron ore s limes from Joda mines of TISCO and Kiriburu mines of SAIL situated in the west Singhbhum district of Bihar, India. Effect of pulp density and dose of flocculant are reported in the present paper.

Experimental Procedure

Materials-Slim~s obtained from desl iming of the ores from Joda mines was used. Mineralogically, it consists of hematite as major phase, quartz , illite and kaolinite as minor phase. Chemical analysis of the slime (in wt.%) was:

• Fe = 56.37% ; Si02 = 7.48% ; AhO) = 7.0 I %

Slimes from the dewatering screen at Kiriburu processing plant was collected and studied. Reflected light microscopic study on the Kiriburu s limes indicated goethite, limonite and hematite as the maj or mineral phases while associated c lay mineral s along with quartz were identified as the s iliceous mineral gangues. Chemical analysis of the s limes ( in wt.%) was:

• Fe = 61.40% ; Si02 = 3.84% ; AI 20 ) = 6.63%

BHAGAT & DEY : FLOCCULATION OF IRON ORE SLIMES 281

'OO~~------------~~~~I -0 0 PPM

~ 10 PPM • 20 PPM .., 30 PPM

00 50 100 ISO 200 250 300 3S0 400

liME,S

Fig. I-Effect of magnafloc lOll dose on Joda slimes at 15% pulp density and neutnil pH.

~

:Ie

!:2 ~ 20

10

00 25 50 75 100 125 150 17S 200 225 250

TtME . S

Fig. 2-Effect of magnafloc lOll dose on Joda slimes at loolo pulp density and neutral pH.

Table 1 shows the size analysis of Joda and Kiriburu slimes measured by WannaTl cyclosizer. The mineralogical constituents of Kiriburu slimes differ from those of Joda slimes. Kiriburu slimes contain quartz (specific gravity 2.60) whereas Joda slimes contain alumino-silicate minerals (specific gravity less than 2.60) as minor phase. The Kiriburu slimes contain hydroxides (goethite/limonite) as major phase besides hematite which only occurs in Joda slimes. A signjficant difference in the mineralogical constituents of these sample has resulted in the difference in zeta potential values. The Joda slimes is more electronegative (zeta pot. -37.9 mY) at neutral pH than Kiriburu slimes (zeta pot. - 23.5 mY) .

Magnafloc 1011- a high molecular weight anionic flocculant was used . As per technical specificati on

Table I--Sieve analysis of Joda and Kiriburu slimes

Joda Slime Kiriburu Slime Size in micron Wt.% Size in micron Wt. %

+30.01 5.64 +28.95 45 .73 -30.01+20.82 5.17 - 28.95+20.08 12.45 -20.82+ 14.65 7.61 - 20.08+ 14.13 10.82 -14.65+ \0.03 9.35 -14.13+9.67 7.72 -10.03+8.\0 11.33 -9.67+7.81 2.95

- 8.10 60.90 ' -7.81 20.33 Total 100.00 Total 100.00

provided by the manufacturer (TDP 10 11 , Ref. 280117870, Allied Colloids, UK) it is white granular powder with particle size 98% less than 1000 micron . Its viscosity values at different shear rates and concentrations are mentioned in the specification.

Methods-The settling test was carried out in a batch 100 rnL graduated cylinders with stoppers. 100 mL of suspension of desired concentration was taken in a cylinder. Required dose of the flocculant was added to it from the stock solution . The suspension was dispersed by inverting the cylinder up and down ten times. The settling rate of particles was measured by noting down the movement of suspension/water interface as a function of time till there is no further downward movement of particles indicating the end of settling. The plots were made against height of interface versus time. Height of interface (in mm) is calculated from volume in mL divided by the conversion factor of the cylinder which was 1.62.

Results and Discussion The kinetics of settling of fine particles is

influenced by the quantity of the flocculant, pulp density, and types of the minerals present in the slimes.

Effect of jlocculant quantity-Plots of height of interface agai nst time at neutral pH in case of Joda slimes are shown in Figs I and 2 respectively for fifteen percent and ten percent pulp · densities. The effect of flocculant quantity on settling characteristic is indicated in these fi gures. T he flocculant dose is reported as ppm (equivalent to g/ton) , weight basis for all sets of experiments. An increase in the settling rate with increasing amount of the flocculant in the suspension is attributed to the increasing numbers of amide and hydroxyl groups available to be adsorbed on the partic les and make bridges with them. Simi lar trends have been observed by the previous authors3

•13

.

An optimum amount is generally recommended which varies from system-to-system.

282 INDIAN J. ClffiM. TECHNOL., SEPTEMBER 1999

..... 30 :I: ~

20 UJ :I:

to

0 0 25 50 75 too t25 !SO 175 200

TIME., S

Fig. J-Effect ofmagnafloc 1011 dose on Kiriburu slimes at 15% pulp density and neutral pH.

~ ~ <"oj"

~ r

--UJ u

!i ..... ~~ :> ..j'" 00 >0-

:I:

~

100------------------,

&0

70

60

50

40

30

20

10

0 0

, ! ,

. 0 10", PO

• IS %" PO .... 20%'PO

50 toO ISO 200 250 300 350 400 450

TIME,S

Fig.4-Effect of pulp density on Joda slimes with magnafloc 1011 at 10 ppm and neutral pH.

A comparison of Figs 1 and 2 reveals that the effect of flocculant dose is more pronounced at lower pulp density. The dilution of slurry has positive effect as regards faster settling is concerned and this is being practised in one of the TiSeO mines l4

. The flocculant can move with greater ease when the suspension is diluted which results in their higher approachability towards particles and better adsorption.

It is apparent from Figs I and 2 that the rate of settling is maximum initially and decreases till a situation which has been previously referred as transition zone, beyond which compression zone starts where fall of the suspension··water interface is almost plug type lS

• This is in particular applicable

~ ~ ",'

~

'-.., -'U

~~ ..,.., ~-

~~ 0-X \2 .., x

-0- 10~ PD ~ 2O%PO .... 30% PO

70 .0-40 X PO

60

50

40

30

~~~5~0--~1~OO~~1~50~-200~--2~~--~300---J3~ TIME,S

Fig. 5--Effect of pulp density on Kiriburu slimes with magnafloc 10 II at 5 ppm and neutral pH.

when flocculant is added. The partides settle at almost constant rate during the entire period of settling when no flocculant is added to it (0 ppm) .

Fig. 3 shows the effect of flocculant dose on settling rate of Kiriburu slimes at 15% pulp density and neutral pH. The settling rate of Kiriburu slimes was fast, therefore the effect of flocculant dose was studied at lower values. Unlike Joda slimes, the Kiriburu slimes settles almost linear up to maximum of the column height followed by abrupt compression of the settling zone.

Effect of Pulp Density-Fig. 4 shows the effect of pulp density on the settling rate at 10 ppm flocculant dose in case of Joda slimes.The initial settling rate decreases with increasing pulp density. This can be ascribed to a greater buoyancy as well as lesser ease of liquid trickling through particles (at higher pulp density) . It is apparent from Fig. 4 that at 20% pulp density the particles settle with . almost constant rate whereas the two zones of settling: linear and compressed ones are distinctly visible at 10% pulp density. Fig. 5 shows the settling data in case of Kiriburu slimes at 5 ppm flocculant dose and neutral pH. It is apparent from Fig. 5 that the difference between the settling rate when the pulp density was changed from 10% to 20% was less than that when the pulp density was changed from 30% to 40%. In this case also the two zones of settling are more distinctly visible at lower pulp density.

Flocculation of Joda slimes vis-a-vis Kiriburu slimes

Fig. 6 typically compares the settling data of Joda slimes with Kiriburu slime at natural pH and fifteen

BHAGAT & DEY : FLOCCULATION OF IRON ORE SLIMES 283

-0- JClC¥I SUME

K1R1BlRJ SUME

00 50 100 150 200 250 300 350 400

l iME,S

Fig. &-Effect of mineral type with magnaOoc 1011 at 15% pulp density and 10 ppm Oocculant dose.

percent pulp density. The flocculant quantity was fixed at 10 ppm. It is apparent that the' settling of particles is considerably faster in case of Kiriburu slimes than that in case of Joda slimes. In general, the settling of particles is affected by their particle size, specific gravity, and electrical nature as well as environment of the aqueous phase. A difference in the settling rate in case of two types of slimes was also observed when no floccu lant was used. This could be attributed to the following facto rs in this case: • It is apparent from Table I that -8 micron size

fraction in Joda slimes is 60% compareQ to 20% in case ofKiriburu slimes.

• Kiriburu slimes, having specific gravity of 3.5 18 was slightly denser than the Joda slimes wh ich has specific gravity of3.445.

• The stability of Joda slimes is higher due to higher amount of electronegative charge on its surface at neutral pH compared to Kiriburu slimes. Unlike Kiriburu slimes, the supernatant was hazy

and oozing was also observed through the settled particles in case of Joda sl imes. This could be attributed to the presence of higher clay mi nerals in it. This has also resulted in lesser settling rate in case of Joda slimes when compared with Kiriburu sl imes.

Conclusions (a) The present investigation has shown that the

sedimentation rate increases with increasi ng the flocculant dose up to a certain limiting value, after which the improvement is marginal. This phenomenon suggests an optimum level for the

sedimentation following flocculation. Keeping economy in flocculant consumption in view, a flocculant dose of 20 ppm has been considered reasonably good for faster settling of particles in case of Kiriburu and Joda slimes.

(b) The settling rate decreases with increasing the pulp density. A variation in the flocculant dose has more pronounced effect on the settling rate at 10% pulp density as compared to higher ones.

(c) Kiriburu slimes settle faster than Joda slimes. This may be attributed to: • difference in size, • difference in density of these particles, and • difference in mineralogical constituents present in these samples which significantly influence the electrical nature of the particles as well as the conformation of the polymer when adsorbed onto their surfaces.

(d) Plug type settling (with constant rate) is observed when pulp density of the suspension is higher (20%) orland when there is no flocculant added into the suspension . There happens to be abrupt change in the settling rate (the compression zone starts soon after linear settling rate zone) in case of settling of particles in the suspension at lower pulp density ( 10%) orland higher dose of flocculant.

Acknowledgement

The authors thank Prof. P. Ramachandra Rao, Di rector, National Metallurgical Laboratory, Jamshedpur for providing laboratory facility, and support. Mr. S C Maulik and Prof. R P Singh are also thanked for useful discussion.

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284 INDIAN 1. CHEM. TECHNOL. , SEPTEMBER 1999

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