Manufacturing of ceramic products using calamine hydrometallurgical processing wastes

Highlights

• Physico-chemical characteristics of raw and fired calamine wastes are described.

• Ceramic materials are prepared by firing calamine tailings at 1050 °C.

• Sintering is enhanced in samples containing high amounts of fluxing agents.

• Heavy metals are mostly immobilized during firing process.

Abstract

Because of the physical, chemical and environmental risks related to industrial wastes and the high consumption of finite natural resources in the construction industry, this paper presents an ecological and sustainable way to manufacture ceramic products using calamine hydrometallurgical processing wastes. This process generates a by-product called herein calamine process tailings (CPMT). Moreover, a sample of treated calamine process tailings (TCPMT) with low amounts of lead was also studied. The aim of this study is to characterize both wastes in order to assess the feasibility of their reuse potential as ceramic alternative materials. The effect of firing temperature on the chemical, mineralogical, environmental behaviors and the physical and mechanical properties of ceramic samples as well as the characterization of the fumes released during firing process are assessed. The results showed that increasing firing temperature enhances the flexural strength of ceramic samples and decreases their open porosity and water absorption. The TCPMT ceramic samples showed very different physical and mechanical properties in comparison with those made with CPMT. These latter samples present high flexural strength values and very low level of water absorption when fired at 1050 °C. This difference might be attributed to high amounts of glassy phase produced in CPMT fired samples. Moreover, the amount of leached metals is reduced significantly after the thermal treatment. However, arsenic, which was in a non-leachable form in the green samples, was found to be leached when tailings are fired. The scanning electron microscopy analysis (SEM-EDS) of condensed fumes evolved during the thermal treatment shows that lead is slightly volatilized.

Introduction

One of the ongoing worldwide concerns, from an economic and environmental point of view, is the management of high amounts of industrial and mine wastes daily generated. This concern continuously grows due to different reasons: (i) the scarcity of available spaces to dispose wastes, (ii) the negative environmental impact of some wastes, (iii) the increasing pressure on disposal alternatives, and (iv) the high rate of finite natural resources consumption (clays silts, sand, aggregates, etc.) mainly as construction materials. These finite resources are becoming increasingly scarce and many governments across the planet try to limit their exploitation. For example, the Chinese government has already forbidden in many regions the production of solid bricks using natural clay (Yang et al., 2014). In the recent decades, the need to develop reliable, economic and feasible environmental methods is increasingly growing. An emerging key approach to solve this question was developed recently and defined as industrial ecology. This latter aims at establishing closed loop cycles in order to minimize wastes generation and optimize energy and materials consumption (O'Rourke et al., 1996). Wastes are then considered as alternative materials that could feed other industries.

Zinc is one of the non-ferrous metals widely used in various applications: galvanizing industries, batteries and rubber manufacturing industries, cosmetics, construction and renovation, etc. The production of zinc in Morocco is estimated at 91,600 t in 2012 (MEMEE, 2012). Zinc is extracted mainly from sulfides and oxidized zinc ores. Currently, a hydrometallurgical process, using sulfuric acid, is used to produce 75% of the world's zinc from roasted zinc sulfide (Montanaro et al., 2001). In this case, the zinc extraction process produces large amounts of wastes containing mainly iron hydroxides/oxides in the form of jarosite (KFe₃(SO₄)₂(OH)₆), goethite (FeOOH) or hematite (Fe₂O₃) (Asokan et al., 2010, Pelino et al., 1996, Romero and Rincón, 1997).

Calamine hydrometallurgical processing (CHP) is a direct sulfuric acid leaching method used to recover zinc from oxidized zinc ores. The term “calamine” derives from a location in Belgium and has no real mineralogical significance. The most known economic Zn-minerals are smithsonite (ZnCO₃), hydrozincite (2ZnCO₃·3Zn(OH)₂), zincite (ZnO), willemite (Zn₂SiO₄) and hemimorphite (Zn₄Si₂O₇(OH)₂·(H₂O)). During CHP, wastes called calamine process mine tailings (CPMT) are produced; they are mainly composed of gypsum and lesser amounts of iron hydroxides. Gypsum waste is a by-product of sulfuric acid dissolution of carbonate minerals, mainly calcite and dolomite. Gypsum waste has been widely reported in the literature. Various types of this waste are produced by several industries such as: phosphogypsum from phosphoric acid industry (Ajam et al., 2009, Garg et al., 2009, Singh, 2005), nitrogypsum from nitrocellulose industry (Marinkovi et al., 2004), flue gas desulphurization (FGD) gypsum from FGD industry (Guo and Shi, 2008), borogypsum from boric acid industry (Emrullahoglu Abi, 2014), fluorogypsum from hydrofluoric acid industry (Garg and Pundir, 2014) and tartarogypsum from tartaric acid industry (Bensted, 1981). Several studies have assessed the potential use of gypsum wastes to produce construction and building products. The gypsum wastes are used as a component in composite binders (Garg and Pundir, 2014), as a substitute material in brick making (Emrullahoglu Abi, 2014, Mymrin et al., 2015) and as an additive material in earthwork projects (San-Antonio-González et al., 2015). Furthermore, gypsum wastes are evaluated to synthesize calcium carbonate and elemental sulfur (de Beer et al., 2015), to synthesize nanostructured hydroxyapatite for the removal of Pb and Cd from wastewater (Yan et al., 2014) and to prepare ceramic blocks (Godinho-Castro et al., 2012). They can also be used to manufacture lightweight materials (San-Antonio-González et al., 2015), to produce cement and concrete products (Garg et al., 2009, Gazquez et al., 2013, Guo and Shi, 2008, Jarosiński, 1994, Shen et al., 2013, Singh and Garg, 2000), and finally to produce plaster products (Marinkovi et al., 2004, Singh, 2005).

However, before considering the valorization of any waste, some challenges related to transportation, processing and commercialization of the valorized products should be dealt with. Transport costs present the biggest challenge for waste producers and potential consumers. That is why it is crucial to consider possible options for reducing these costs. The use of these tailings as fine aggregates to manufacture mortar and concrete (cement based products) was assessed in the first place. However, results of this study were not encouraging. Characterization tests showed that some constraints linked to the hydration mechanisms were observed. This was explained by the presence of some pollutants such as Zn and Pb which are considered as setting retarders. So, it was important to find another way of valorization.

In this study, the feasibility to produce ceramic materials from calamine process mine tailings is assessed. Ceramic industry was chosen due to high demand on ceramic products and because Marrakech city is one of the main centers of pottery and ceramic production in Morocco. Nevertheless, no study has been made to characterize and determine the sintering behavior of CPMT for investigating their potential reuse as ceramic materials. Due to their content in fluxing agents (K₂O, Na₂O, PbO); which can decrease the sintering temperature, promote the formation of silicated liquid and reduce the costs of firing process (Grimshaw and Searle, 1971, Quijorna et al., 2014), these wastes may be used as ceramic materials. This study aims at providing a physical, chemical, mineralogical and environmental characterizations of unfired and fired tailings, an analysis of their thermal behavior during firing process, an assessment of the physical, mechanical and environmental properties of fired samples and finally a characterization of the released fumes during the production process.