Application of microwave irradiation to quick leach of zinc silicate ore

doi:10.1016/S0892-6875(02)00050-X

Minerals Engineering

Volume 15, Issue 6, June 2002, Pages 451-456

https://doi.org/10.1016/S0892-6875(02)00050-X Get rights and content

Abstract

A zinc silicate ore was treated with sulfuric acid in a water-starved system in the presence of microwave irradiation. Phase changes occurring during the reaction process were examined by X-ray powder diffraction analysis, and the effect of microwave irradiation time and water amount used on the extraction of zinc, silica and iron was investigated. It is demonstrated that the hemimorphite present in the ore is predominantly changed to ZnSO₄·6H₂O for samples without microwave irradiation and ZnSO₄·H₂O for those with microwave irradiation, respectively. Silica and iron are changed to quartz and Fe(OH)₃. An increase in microwave irradiation time can slightly increase the extraction of zinc and decrease the dissolution of iron. The increase of water amount used can increase the extraction of zinc and considerably decrease the dissolution of silica. Under optimum conditions, the extraction percentage of zinc is 99.08% and the dissolution of silica and iron is as low as 0.30% and 0.10%.

Introduction

Zinc silicate ores are attractive alternatives to zinc sulfide ores for the extraction of zinc owing to the increased restriction on sulfur emission all over the world. However, this attractive zinc resource is not widely used for lack of suitable processing methods. The zinc silicate ores usually have a low content of zinc and a high content of silica. The low zinc grade of the ores results in high consumption of energy in pyrometallurgical processing due to the necessity of heating high contents of gangue materials. The high content of silica usually enters solution as silica gel with zinc when hydrometallurgical method is used. The formation of silica gel makes filtration difficult. Form the economy point of view, hydrometallurgical methods are more attractive than pyrometallurgical ones for the treatment of zinc silicate ores, especially for low grade ores. The problem is that the silica gel formed during sulfuric acid leaching should be prevented. To overcome the filtration difficulty, a new flocculating agent (Magnafloc 156) was used by Bodas (1996) and the quantity required was very small compared to the other flocculating agents used. A method proposed by Ikenobu (2000) made it possible to precipitate silica in a form having excellent solid–liquid separation characteristics, without the need for facilities having a high filtration capacity, and to maintain a low silica concentration in the solution by feeding a compound containing pre-adjusted silica contents. Perry (1966) used Al₂(SO₄)₃ as the flocculating agent to prevent clogging of the filters with silicic acid. However, the use of Al₂(SO₄)₃ made the leaching process rather complicated. Matthew and Elsner (1977) adjusted the pH of the leach solution to 4–5.5, using a neutralizing agent, to precipitate and coagulate the collodial SiO₂. In these processes the operating parameters must be properly controlled, otherwise collodial silica will not be effectively precipitated from the solution. For the effective control of silica gel, Dufresne (1976) presented a method of treating zinc silicate ores, called the quick leach. It was based on the chemistry of a water-starved system and effectively rejected silica from many silicate minerals. This method was simple and reliable. The quick leaching method was also applied to an Egyptian zinc silicate ore by Abdel-Aal and Shukry (1997). The dissolution of silica could be appreciably reduced by the quick leach. The problem is that the dissolution of iron was as high as 40–72% (Dufresne, 1976). The increase of the water amount used during quick leach could reduce the dissolution of iron, but this would result in an increase in the dissolution of silica. In this paper, as a fundamental study, the microwave irradiation has been applied to the quick leach of a Yunnan (China) zinc silicate ore to increase the extraction of zinc and reduce the dissolution of silica and iron.

Section snippets

Materials

The zinc silicate ore used in the present study was from Yunnan Province of China. The ore was ground to less than125 μm in a ball grinder. The ore ground was analyzed by chemical method and examined by X-ray powder diffraction (XRD). The chemical composition of the ore is given in Table 1 and the XRD pattern of the ore is shown in Fig. 1. It is indicated from the XRD analysis that the major minerals present in the ore are hemimorphite Zn₄Si₂O₇(OH)₂H₂O and quartz SiO₂.

The sulfuric acid used has

Microwave heating characteristics of zinc silicate ore and related compounds

Microwave heating is different from conventional heating. The temperatures reached by microwave heating, to a large extend, depend on the properties of materials. It is necessary to measure the microwave heating characteristics of the zinc ore and the related compounds for the better understanding of reaction mechanism. Fifty grams of powder sample was placed in a quartz crucible and then subjected to microwave irradiation for 10 min. After microwave irradiation had stopped, a thermocouple was

Conclusions

(1) The silicate ore and the related compounds can be heat to different temperatures by microwaves, but the temperatures reached are below 176 °C. The reactions can proceed at low temperatures when microwave irradiation is used. It is favorable for the reduction of energy consumption.

(2) The hemimorphite present in the zinc silicate ore is predominantly transformed into ZnSO₄·6H₂O for the samples without microwave irradiation and ZnSO₄·H₂O for those with microwave irradiation, respectively. The

Acknowledgements

The authors gratefully acknowledge the Natural Science Foundation of Yunnan Province for the financial support of this work (Project No. 2000E0028M).

References (8)

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Application of quick leaching method to an Egyptian zinc silicate ore
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M.G. Bodas
Hydrometallurgical treatment of zinc silicate ore from Thailand
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R.E. Dufresne
Quick leach of siliceous zinc ore
Journal of Metals
(1976)
Y. Hua et al.
Heating rate of minerals and compounds in microwave field
Transactions of Nonferrous Metals Society of China
(1996)

There are more references available in the full text version of this article.

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Technical NoteApplication of microwave irradiation to quick leach of zinc silicate ore

Abstract

Introduction

Section snippets

Materials

Microwave heating characteristics of zinc silicate ore and related compounds

Conclusions

Acknowledgements

Application of quick leaching method to an Egyptian zinc silicate ore

Transactions of the Institution of Mining and Metallurgy (Section C: Mineral Processing and Extractive Metallurgy)

Hydrometallurgical treatment of zinc silicate ore from Thailand

Hydrometallurgy

Quick leach of siliceous zinc ore

Journal of Metals

Heating rate of minerals and compounds in microwave field

Transactions of Nonferrous Metals Society of China

Technical Note
Application of microwave irradiation to quick leach of zinc silicate ore