Settling and filtration characteristics of manganese nodule leach slurry

The Chemical Engineering

and Filtration

Settling

I. N.

BHATTACHARYA,

Regional

Journal,

Research

38 (1988)

143

143 - 148

Characteristics

of Manganese Nodule Leach Slurry

S. C. DAS and D. PANDA

Laboratory,

Bhubaneswar

751013

(India)

(Received January 14, 1987)

ABSTRACT

Sedimentation and filtration studies were carried out with manganese nodule leach slurry of Indian Ocean origin. Vacuum filtration tests gave better results than the settling tests. The filtration tests were found to follow the intermediate blocking law model. However, at higher concentrations and relatively higher pressures the cake filtration law was found to be valid. The data thus generated should be useful in designing an appropriate separation circuit.

1. INTRODUCTION

Ocean nodules represent one of the world’s most abundant sources of non-ferrous metals existing today. The nickel, copper, cobalt and manganese present in these nodules could well meet the world’s demand for these strategic metals in future. Because of the high moisture content of the nodules and their non-amenability to physical beneficiation, hydrometallurgical process routes are normally favoured for extraction of these metals. There are several processes [ 1 - 61 being developed for extracting these valued metals from nodules of Pacific and Atlantic Ocean origin. Although some information is available on leaching, solution treatment etc., no systematic data on solid-liquid separation are available. However, Agarwal et al. [5,6] reported using thickeners for separating the leach slurry, though no detailed information was given. The U.S. Bureau of Mines [7] reported laboratory-scale solid-liquid separation experiments and also proposed some operational details. At the Regional Research Laboratory, Bhubaneswar, a number of process routes [8 - 111 have been standardized for extracting metals from nodules from 0300-9467/88$3.50

the Indian Ocean. One of these processes involves aqueous reduction of nodules with ferrous sulphate in an ammoniacal medium [ 111. The present work is an examination of the solid-liquid separation behaviour of the slurry obtained after ferrous sulphate reduction of manganese nodules.

2. EXPERIMENTAL

DETAILS

Settling and filtration experiments were carried out with ammoniacal leach slurry containing mainly copper, nickel, cobalt, iron and manganese in the filtrate. X-ray diffraction study of the residue showed iron hydroxide, ferric oxide, ferrous oxide, silica, manganese monoxide and manganese dioxide. All the settling experiments were carried out in 1000 ml graduated cylinders with 5%, lo%, 15% and 20% pulp density slurry. The hindered settling data and the final settled concentration in each case were recorded. The filtration tests were carried out in a standard vacuum leaf filtration unit, employing a Buchner funnel of 10 cm diameter fitted with a filter cloth (pore size, 15 20 pm) and connected to a graduated cylinder for filtrate collection. A pressure difference through the filter media of 18 to 62 cm of mercury was maintained at a constant level by using a vacuum pump during each experiment. The volume of suspension used in each experiment was 500 cm3. Three different pulp densities, namely 20%, 55% and 65% were taken. These slurries were prepared by adding the required amount of residue to the as-received slurry. Data on filtrate volume were noted at diffe_rent times. The particle size distribution of the slurry was determined by the wet sieving method and is shown in Table 1. The viscosity of different slurries was 0

Elsevier Sequoia/Printed

in The Netherlands

144 TABLE

1

Particle

size distribution

Mn

LEACH

NODULE

SLURRY

loo-

of the leach residue

--.

Proportion (%)

Size of particles (Pm)

retained $

1.0603

300 210 180 53 <53

. .

80-

‘0

60-

/

I:

25.058 0 48.09 25.79

s 40 -

20 -

0

measured using a HAAKE RV 100 rotational viscometer with MV II spindle.

0

I 5

I 10 PULP

15

20

Fig. 2. Maximum solid concentration pulp density slurries. 3. RESULTS

of different

AND DISCUSSION

The results from solid-liquid separation studies using the ammoniacal slurry obtained from the treatment of manganese nodules are reported in the present paper. The settling and filtration characteristics of the slurry are compared and the slurry characterized. An attempt is also made to fit the filtration data to the blocking filtration model. 3.1. Comparison of settling and filtration Figure 1 shows settling curves for slurries containing solids in the range 5 - 20 wt.%. These are the probable solid concentrations in slurries obtained from the test plant after leaching the nodules. It may be noticed from Fig. 1 that the time taken to reach minimum

35+

5

DENSITY

Mn NODULE

LEACH

PULP A:

I 60

SLURRY

DENSITY 5

B.

Hn NODULE 14

w

I 180

240

I 300

I 360

I 420

LEACH

DENSITY

SLURRY

20 %

curves for different

, LB0 VOLUME

TIME,min

Fig. 1. Settling slurries.

PULP

on OF Hg

10 x

I 120

settling rate increases with an increase in pulp density. The maximum solid concentrations (C, max.) of these samples are shown in Fig. 2. The filtration tests were carried out using three different slurry concentrations, namely 20%, the as-received concentration from the plant; an intermediate concentration reached after settling the 20% slurry beyond the constant-rate period, i.e. 55%; and 65% slurry obtained after nearly reaching equilibrium. The filtration curves (t us. u) for the 20% slurry at different pressures are given in Fig. 3, which shows an increase in filtration rate with pressure. Figure 4 shows a comparison of filtration and settling tests on a unit area basis. This

pulp density

Ic.c.1

Fig. 3. Filtration curves for 20% pulp density at different constant pressures.

slurry

145 Mn PULP

-

NODULE

LEACH

generalized power-law equation can be fitted to these types of slurries:

SLURRY

A:

DENSITY 20 K

cm OF Hg

8:

20 w

16

c:

20 x

30.5

#,

8,

0:

20 x

10

I,

#,

SETTLING FILTRATION

CURVE

r=ro+KD”

CURVE

(1)

where r is the shear stress (Pa); ro, the yield stress (Pa); K, the fluid consistency index; n, the flow behaviour index and D, the shear rate (s-i). For a Bingham fluid

6-

r=ro+KD A

(2)

and for a newtonian fluid r=KD

I

0

5

10

15

TIHE,min.

Fig. 4. Comparison of curves for filtration and settling.

indicates that the filtration rate is 4 to 5 times higher than the corresponding settling rate. 3.2. Characterization of the slurry used The nodule slurry of pulp density around 20% shows newtonian behaviour but slurries of high pulp densities show non-newtonian behaviour (Fig. 5). It is observed that 55% slurry shows Bingham plastic behaviour whereas slurry of about 65% shows pseudoplastic characteristics. The stresstime plot shows no change of stress value with time thus indicating no thixotropic effect. A

The K and n values for different pulp densities are calculated using eqns. (1) - (3) and are reported in Table 2. TABLE 2 Variation of K and n values with solid concentration Pulp density WI

K (Pa sn)

n

20 55 65

0.0139 0.00714 5.10

1 1 0.6214

3.3. Analysis of the filtration data The filtration data are analysed in the light of blocking laws. The mechanisms of blocking laws are based on pore sealing as well as on the probability of pore blocking involving geometric considerations as to particles and filter membrane interaction [ 121. Blocking laws were studied first by Hermans and Bredee [13] and further modified by Gonsalves [ 141, Grace [ 151, Hermia [ 161 and Shirato et al. [17]. The characteristic form of the blocking filtration laws may be expressed as d2t

-=

du2

60 STRAIN,

60 D

100

ISec-‘I

Fig. 5. Stress vs. strain curves for different pulp density slurries.

(3)

(4)

for constant pressure filtration [ 121. Further, the filtration laws are subdivided into four different categories depending upon the numerical value of n’ and these may be written as (i) when n’ = 1, corresponding to the intermediate blocking law;

146

(ii) when n’ = 1.5, corresponding to the standard blocking law ; (iii) when n’ = 2, corresponding to the complete blocking law; (iv) when n’ = 0, corresponding to the cake filtration law ; where K’ and n’ are constants related to the parameters which define the rheological properties of the fluid. For a constant-pressure filtration the “resistance coefficient” can be defined as the rate of variation with respect to filtrate volume of the instantaneous resistance to filtration which can be measured as the inverse of the flow rate: d 1 d2t -=du 0Q du2

Mn NODULE LEACH SLURRY PULP DENSITY: 55 y.

14 -

12-

A

:

8

:

C

:

:

NOOULE

LEACH

DENSITY

A:

LO cmOF

6:

62cmOFHg

SLURRY

: 65 % Hg

A

1‘

Fig. 7. Filtration curves for 65% pulp density slurry at different constant pressures.

Hn

NOOULE PULP

D:

LEACH

SLURRY

DENSITY 20 w

cm

OF

“g

CO

5s x

(0

65 X 65%

40 62

3.0-

2.5-

2.0;;P

1

C 01

10-

0

1

so

100

150 VOLUME

I

200 lc.c.1

250

300

7&--z

Fig. 8. Plot of inverse of flow rate us. volume of different pulp density slurries at different constant pressures.

0

I

0

PULP

(5)

where Q is the flow rate. Figures 3, 6 and 7 respectively are filtration plots for 20%, 55% and 65% pulp density slurries at different pressures, showing an increase in the filtration rate with increase in pressure. A plot of the inverse of the flow rate (dt/du) against the volume of filtrate collected is shown in Fig. 8, where a deviation from linearity at a pressure of 40 cm of mercury is observed (curves A, B and C). This also occurs at other pressures, but for 65% pulp density slurry at a higher pressure i.e. 62 cm of mercury (curve D), the graph is linear. The plots of d2t/du2 us. dt/du for 20% and 55%

l6

Mn 16

50

,

I

100 150 VOLUME

200

250

300

Ic.c.1

Fig. 6. Filtration curves for 55% pulp density slurry at different constant pressures.

pulp density slurry (Figs. 9 and 10) at three different pressures indicate that the resistance coefficient varies linearly with the instantaneous resistance to filtration. In the case of 65% pulp density slurry (Fig. 11) at a lower pressure, i.e. 40 cm of mercury, the same pattern is followed. But at a higher pressure, i.e. 62 cm of mercury, the resistance coefficient is found to be constant. The plots of d2t/du2 us. dt/du (Figs. 9 - 11) show linearity,

147

:;I, , , , , , , 0

0.2

0.4

0.3

0.6

1.0

1.2

1.6

dt/dv

Fig. 9. Plots of resistance coefficient with inverse flow rate for 20% pulp density slurry at different constant pressures.

Mn NODULE LEACH SLURRY PULP DENSITY 55% 2.0-

cm

AI B:

OF 16

tig

A

40

thus indicating the index n’ to be unity. But the slurry of 65% pulp density shows a deviation from the above observations at a higher pressure (62 cm of mercury). In this case the value of n’ is equal to zero. So in all the cases the filtration follows an intermediate blocking law except for that at higher pulp density and higher pressure. In this case it obeys the cake filtration law. At low concentrations newtonian behaviour predominates. Particles are discrete and move at random. So in this case, particles probably participate in blocking some of the pores as well as settling on other particles. But in higher concentration slurries at higher pressures a settled bed immediately forms over the septum, becoming the cake upon which other particles fall, facilitating further cake formation. It may be recalled that in a pseudoplastic fluid which can be easily deformed by local shear, cake formation is more of a possibility than in its counterpart when it is a Bingham fluid.

c:

1.6 -

N> 1.2 w

4. CONCLUSIONS

z D 0.6 -

0.4

0.6

1.6

1.2

2.0

2.4

2.6

dt/dv

Fig. 10. Plots of resistance coefficient with inverse flow rate for 55% pulp density slurry at different constant pressures.

-._

Mn NODULE LEACH SLURRY PULP OENSITY : 65 X

2.0-

(1) The filtration rate of manganese nodule leach slurry in ammoniacal media is higher than the rate of settling. (2) The behaviour of the slurry at low solid concentrations (20% pulp density) is newtonian while at higher solid concentrations (55% and 65% pulp density), it is successively Bingham plastic and pseudoplastic. (3) The filtration mechanism can be explained by applying the intermediate blocking filtration model except at higher concentrations and higher pressures where it follows the cake filtration law.

ACKNOWLEDGMENTS

a4

-

0 0

I 0.L

I 0.6

I 1.2

I 1.6

1 2.0

2.4

2.3

dt /dv

Fig. 11. Plots of resistance coefficient with inverse flow rate for 65% pulp density slurry at different constant pressures.

The authors are grateful to Prof. P. K. Jena, Director, for his keen interest in the work and permission to publish this paper. They are also grateful to Dr. R. P. Das, Project Coordinator of Hydro and Electrometalhugy Division, for his encouragement during the work and valuable discussions.

148 REFERENCES 1 R. R. Beek and M. E. Messner, in R. P. Ehrlich (ed.), Copper Metallurgy, Metallurgical Society of AIME, New York, 1970, pp. 70 - 83. 2 K. N. Han and D. W. Fuerstenau, Int. J. Miner. Process., 1 (3) (1974). 3 G. Hanig, in C. Kruppa (ed.), Interocean ‘73, 1 (1973) 432 - 444. 4 K. H. Ulrich, U. Scheffler and M. J. Meixner, in C. Kruppa (ed.), Interocean ‘73, 1 (1973) 445 - 457. 5 J. C. Agarwal, N. Beecher, D. S. Davies, G. L. Hubred, V. K. Kakaria and R. N. Kust, J. Met., 28 (1976) 24 - 31. 6 J. C. Agarwal, H. E. Barner, N. Beecher, D. S. Davies and R. N. Kust, Trans. Sot. Min. Eng. AIME, 31 (1979) 1704 - 1707. 7 B. W. Haynes, S. L. Law, D. C. Barrow, G. W. Kramer, R. Maeda and M. J. Magyar, U.S. Dept. of the Interior Bureau of Mines, Bull. no. 679, 1985. 8 R. P. Das, S. Anand, S. C. Das and P. K. Jena, Hydrometallurgy, 16 (1986) 335 - 344.

9 S. C. Das, S. Anand, R. P. Das and P. K. Jena, Leaching studies on Indian Ocean manganese nodules in dilute sulphuric acid using carbon as a reductant for extraction of copper, nickel, cobalt and manganese, Aust. J. Min. Metall., accepted for publication. 10 S. Anand, S. C. Das, R. P. Das and P. K. Jena, Leaching of manganese nodules at elevated temperature and pressure in presence of oxygen, Hydrometallurgy, accepted for publication. 11 S. Anand, S. C. Das, R. P. Das and P. K. Jena, Leaching of manganese nodules in ammoniacal media using ferrous sulphate as reductant, Metall. Trans. B, 19 (1988) 331 - 334. 12 J. Hermia, Trans. Inst. Chem. Eng., 60 (1982) 183 - 187. 13 P. H. Hermans and H. L. Bredee, Reel. Trau. Chim. Pays-Bas, 54 (1935) 680. 14 V. E. Gonsalves, Reel. Trav. Chim. Pays-Bas, 69 (1950) 873. 15 H. P. Grace,AZChE J., 2 (1956) 307. 16 J. Hermia, Reu. Univ. Mines, 2 (1966) 45. 17 M. Shirato, T. Aragaki and E. Iritani, J. Chem. Eng. Jpn., 12 (1979) 162.