The Investigation of Optimizing Leaching Efficiency of Al in Secondary Aluminum Dross via Pretreatment Operations

Haigang Feng,Luobing Xun,Qun Yang,Guofan Zhang,Siyuan Zhen,Dezhi Liu

doi:10.3390/pr8101269

Abstract

Secondary aluminum dross (SAD) is an inevitable by-product from the secondary aluminum industry and has caused serious environmental issues. In this study, the effect of pretreatment operations on the subsequent acid leaching operation was studied by process mineralogy, a series of leaching experiments, XRD, and SEM. Leaching results showed that the leaching efficiency of Al in direct acid leaching was only 22.99%. Process mineralogy showed the complex intertexture and continuous network structure in the SAD. Pretreatment operations were extremely efficient in destroying the structure by physical and chemical interaction. Interestingly, by adding the grinding and water leaching operations, the leaching efficiency of total aluminum in the SAD reached approximately 28.70%. XRD results showed that nearly all metallic Al, AlN, and partial Al2O3 were leached by grinding–water leaching–acid leaching. The scanning electron micrographs showed that the residue particles mainly included some insoluble components and had a smooth surface.

Highlights

Secondary aluminum dross (SAD), which forms during the aluminum scrap/dross melting processes, is an inevitable by-product from the secondary aluminum industry [1,2]
The leachability of the landfilled SAD normally leads to the leaching of toxic metal ions into ground water, and the high reactivity of the SAD with water can result in the formation of toxic, explosive, and poisonous odorous gases, such as NH3, CH4, PH3, H2, and H2 S [8,9,10]
The results showed that 86–89% of chloride, 54–58% of sodium, and 37–43% of potassium were dissolved during water leaching at 25 ◦ C, whereas only small amounts of the other elements were extracted during the process

Summary

Introduction

Secondary aluminum dross (SAD), which forms during the aluminum scrap/dross melting processes, is an inevitable by-product from the secondary aluminum industry [1,2]. The secondary aluminum industry has been booming in the past few years. With the prosperity of the secondary aluminum industry, more than one million tons of SAD are produced every year worldwide [5]. The SAD typically contains aluminum (Al) metal, aluminum oxide (Al2 O3 ), aluminum nitride (AlN), halite, sylvite, and other contaminants, and these compounds are harmful to the environment and difficult to recover. 95% of the SAD has been stacked and landfilled [6,7]. The toxic metal ions and gaseous emissions from the landfilled SAD is a great environmental concern [8,9,10,11]. Finding a feasible process for treating SAD is imperative

Methods

Results

Conclusion