Zinc Matte를 환원제로 사용한 망간단괴의 침출특성 연구

구성은, 신성혜, 김동수

이화여자대학교 환경공학과

Extraction of Metal Values from Manganese Nodules using

Zinc Matte as a Reducing Agent

Sung-Eun, Kuh, Sung-Hye Shin, Dong-Su Kim

Dept. of Environmental Engineering, Ewha Womans University, Seoul 120-750, Korea

Introduction

Manganese nodules from deep-sea environment found in large quantities, have been focused as valuable resources for Cu, Ni, Co, and Mn, therefore, the extraction of metal values from nodules is significant for the recovery of the resources. Among various hydrometallurgical treatment methods developed for the extraction of a variety of metals from deep-sea nodules, acid leaching has a high reaction rate compared with the alkaline leaching and the acid leaching process, especially using H2SO4, is an inexpensive method and has been adopted generally. Lixiviant is needed to be chemically stable, inexpensive, safe to treat, non-corrosive for the experimental equipment, and easy to collect the reduced metal species, have high solubility for its salt, and dissolve rapidly objective metal selectively. Therefore, leaching with dilute acid solution is considered to be a desirable method, since conventional concentrated acid leaching processes have many drawbacks such as waste acid solution treatment, equipment corrosion and large acid consumption, etc. Dilute acid leaching processes often need some reductants to destroy the mineral structure of the nodules and dissolve the metal values. In recent years, attempts have been made to leach manganese nodules in dilute HCl and H2SO4 with reductants, such as Na2CO3, carbon, pyrite, and copper matte. The authors have been attempting to use several non-ferrous metal sulfides as reductants to leach nodules in dilute acid solutions. It has been demonstrated that the copper matte is an efficient reductant for the leaching of the nodule in dilute HCl solution.

This work reports the reduction leaching behavior of Pacific Ocean nodules with zinc matte as a reductant, which is mainly composed of zinc sulfide in dilute HCl solution.

Experimental

The manganese nodule sample was obtained from the Pacific Ocean at 12 03□north latitude and 139 26□west longtitude at a depth of 4,980 m. The zinc matte was obtained from Chinas Tianshui smelter. The results of chemical analysis by ICP (Perkin Elmer, Optima 3100DV) and XRD (X-ray Diffraction, RIGAKU, X-RAY DIFFRACTOMETER SYSTEM "GEIGERFLEX", D/MAX-RB) of the raw manganese nodules are shown in Table 1. Zinc matte used for reductant in this experiment was analyzed to be composed of 55.1% Zn, 28.9% S, and the 16% rest (SiO2; 10.8%, CaO; 2.7%, Al2O3; 2.3%, MgO; 0.2%).

Table 1. Chemical analysis of the raw materials (wt%).

Materials	MnO2	Fe2O3	SiO2	CaCO3	Al2O3	Ni oxide	Cu oxide	Co oxide	H2O
Manganese nodules	43.20	13.33	19.2	4.1	3.8	1.46	1.41	0.29	13.21

The leaching experiments were carried out in a three-necked round bottom glass flask with a condenser. The agitator and thermostat were attached in this reactor. The reactor contained 300 mL of leachant, which was heated and stirred. The required amounts of powdered nodule and zinc matte, and volume of acid solution were introduced into the flask. The 20 mL of leached solution samples were withdrawn after different periods of leaching, and the contents were filtered, washed with distilled water. The elemental analysis was carried out using the atomic absorption spectrophotometer (Varian, model 1475). The effects of time, acid concentration, temperature, and liquid/solid ratio on the extraction of various metals have been studied.

Results and Discussion

In the HCl solution, the reactions between MnO2 and zinc matte in the presence of iron are as follows:

MnO2 + 2Fe2+ + 4H+ = 2Fe3+ + Mn2+ + 2H2O                 (i)

ZnS + 2Fe3+ = Zn2+ + 2Fe2+ + S0                         (ii)

Figure 1 shows the effect of the leaching time of manganese nodules on the metal extraction. It is found that the extraction of Cu, Co, Mn and Ni reach their equilibrium in about 90 min. More than 99% of Mn was leached in 2M HCl at 70□ for 120 min. The extraction of Ni, Co and Mn were observed to be above 70% after a leaching time of 30 min. Figure 2 shows the effect of the ratio of manganese nodule to zinc matte on the extraction of metal values in 2M HCl at 70□ for 90 min.

Figure 3 shows the effect of HCl concentration at 70□, 2:1 N/R ratio and L/S ratio of 5.5:1 after 90 min of leaching. The term of L/S (liquid/solid) ratio means the lixiviant (HCl solution)/manganese nodule. Figure 4 demonstrates the results for different leaching conditions. This experiment conditions are at 70□C, 3:1 N/R ratio, L/S ratio of 5.5:1, and 60 min leaching time. The extraction of Cu, Mn, Co, and Ni increased with the increase of HCl concentration except in the case of 4M HCl concentration. The reason for this is not clear presently.

Figure 5 shows the effect of temperature on the extraction of metal values in the conditions of 2M HCl, 90 min leaching time, N/R ratio and L/S ratio of 3:1 and 6:1, respectively. Figure 6 represents the change in extraction of Mn according to time at different temperatures in the same conditions of Figure 5. Since the change in extraction in each time range of 0∼5 and 5∼60 min is almost linear, it may be considered that two zeroth order reactions with different rate constants are involved successively in these time ranges. Extraction of Co shows a nearly same trend with that for Mn in the experimental temperature range (Figure 7) and similar extraction tendency with time was also observed for Ni and Cu (results not shown here).

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It has been thought that the L/S ratio has a considerable effect on the extraction of metal values. Figure 9 shows the valuation in the extraction of each metal according to L/S. The extraction of Mn, Co, Ni and Cu increase sharply as the ratio changes from 3 to 6.  The effect of stirring speed on the extraction was observed under the condition of 70□ for 90 min of leaching (Figure 10).

References

1. Parida K., Satapathy P. K., Sahoo A. K., and Das N. J., □Studies on Indian          ocean manganese nodules,□ Colloid. Interface. Sci., 173, 112-118 (1995).

2. Brahim F. B., Mgaidi A., Elmaaoui M., □Kinetics of leaching tunisian phosphate      ore particles in dilute phosphoric acid solutions,□ Canadian J. Chem. Eng., 77,        136-142 (1999).

3. Kai T., Hagiwara T., Haseba H., Takahashi T., □Reduction of thiourea               consumption in gold extraction by acid thiourea solutions,□ Ind. Eng. Chem. Res.,      36, 2757-2759 (1997).