Novel approach for clean utilization of complex low-grade metal resources using silicon as metal getter

Abstract

A method to utilize complex low-grade metal resources cleanly is necessary for the sustainable development of resources and the environment. Si is a widely consumed material in the semiconductor and photovoltaic industries; however, its purity must be upgraded for specific uses. In this study, inexpensive low-purity Si (∼99.32%) was employed as a metal getter to clean accumulated low-grade metal resources by extracting valuable elements from the low-grade resources and to make the manufacture of high-purity Si (∼99.99%) possible. Two common low-grade metal resources were employed in the study as examples: 1) a Ti-bearing blast furnace slag containing Ti and V and 2) a spent automotive catalyst containing Zr, rare-earth elements (Ce, Nd, and La) and platinum group metals (Pt, Pd, and Rh). First, the valuable elements were extracted from the low-grade metal resources using Si to prepare the Si–valuable-element alloy. The extraction process released no carbon gas, because Si acted as both a reductant and a metal getter. Then, the extracted valuable elements were observed to concentrate at the grain boundaries of Si crystals during the solidification process. Finally, the concentrated valuable elements were completely discharged into lixiviants with a minor loss of the Si matrix, i.e., the concentrated valuable elements could be completely separated from the Si matrix through acid leaching. The purity of the Si matrix was significantly enhanced after acid leaching, and high-purity Si was prepared. The high-purity Si, an important high-value byproduct, can be utilized in the semiconductor and photovoltaic industries after further purification or recycled again as a metal getter to treat low-grade metal resources repetitively. This new approach is a promising method for the large-scale treatment of other complex low-grade metal resources.