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1663-014-0108-x  The Minerals, Metals & Materials Society and ASM International 2014

I.

INTRODUCTION

IN recent years, the demand for zinc in China has been increasing steadily.[1] To reduce the production deficit, the production of zinc from hemimorphite (Zn4Si2O7(OH)2Æ H2O) is very relevant in view of the objective situation of increasing shortage of sulfide resources. Hemimorphite as one of the most important zinc resources can be regarded as the exploitable zinc-rich mineral resources.[2,3] There is a great industrial interest in the efficient recovery of zinc from hemimorphite.[4] Despite the zinc-rich silicated mineral resources containing hemimorphite as the major zinc mineral in China, the minerals are rendered unable to be used widely for lack of suitable processing methods.[5,6] The presence of hemimorphite causes serious complications when dissolving said minerals in acid solution because the silicic acid formed by the reaction of sulfuric HONGSHENG XU, ZHIGAN DENG, and XINGBIN LI, Ph.D.’s, CHANG WEI and CUNXIONG LI, Professors, and MINTING LI, Associate Professor, are with the State Key Laboratory of Complex Nonferrous Metal Resources Cleaner Utilization, Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, P.R. China. Contact e-mail: [email protected] Manuscript submitted November 12, 2013. Article published online July 9, 2014. 1622—VOLUME 45B, OCTOBER 2014

acid and hemimorphite is capable of forming a gel, which causes gelation of the solution or significantly increases its viscosity, under certain conditions. This problem impairs or totally disrupts the pulp filtration and limits the mobility of liquid relative to solid phase in the pulp, leading to the reduction of zinc extraction in the solution. To solve the problem above, processing technologies for hemimorphite as the major mineral, especially those using aqueous sulfuric acid as the lixiviant, have been investigated extensively for the recovery of zinc from hemimorphite, such as the use of flocculants,[7,8] microwave radiation,[6] and high-temperature dissolution.[9] Among these methods, high-temperature dissolution technique is considered to be an attractive process in that it is possible to provide good characteristic for solid–liquid separation and extract selectively zinc over silica and iron.[9] In addition, it was reported by Iler[10] that Praetorious and Wolf produced silica sol from gel by heating at 373 K to 573 K (100 C to 300 C) under pressure. However, the behavior of silica sol can change under pressure. This is because the higher process temperatures can accelerate direct dehydration of silicic acid to filterable silica.[9] These findings indicate that using a high-temperature process, it is feasible technique to solve said problems brought on by the formation of silica gel. METALLURGICAL AND MATERIALS TRANSACTIONS B

In the available literature, some investigations have been carried out for understanding the dissolution mechanism of hemimorphite with sulfuric acid solution