*Editorial* **Editorial for Special Issue: "Current Status of Low-Grade Minerals and Mine Wastes Recovery: Reaction Mechanism, Mass Transfer, and Process Control"**

**Shenghua Yin 1,2 and Leiming Wang 1,2,\***


Mineral resources provide an important material foundation for industrial construction and are important for the economy, thus being closely integrated into our daily lives and near future [1,2]. However, mineral resources still possess limitations, such as low mineral grades and serious secondary/concomitant deposits [3]. This undesirable situation causes great difficulty in traditional underground/surface mining, increasing operational costs. In this regard, solution mining (heap leaching, in situ leaching, etc.) offers an environmentally friendly, low-cost, and efficient method for extracting these minerals, especially copper sulfides (chalcopyrite, chalcocite, etc.), sandstone uranium, and sandstone gold deposits. After years of development, solution mining has made great progress, but it has also encountered some technical bottlenecks.

To better understand the current status of low-grade mineral and mine waste recovery, we collected 13 contributions in this Special Issue, whose topics can be divided into the following three main aspects:


Section 1 includes one review paper and three research papers. Nkuma et al. reviewed the metals accessed from low-grade ores and the related environmental impact considerations and then carefully examined the benefits of conventional versus bioleaching strategies [4]. Dushyantha et al. presented a case of mine waste management related to the recovery potential of rare earth elements (REEs) from the gem mining waste of Sri Lanka [5]. Rakishev et al. sought to improve the efficiency of downhole uranium production using oxygen as an oxidizer [6]. Han et al. revealed the flocculation and settlement characteristics of ultrafine tailings and microscopic characteristics of flocs [7]. Section 2 includes four research papers. Alfonso et al. detected the process mineralogy of tailings from Llallagua and discussed the recovery potential of tin reserves [8]; Chen et al. studied the mineralogical characteristics of pegmatite tailings and performed a beneficiation assessment of pollucite in the recovery of cesium [9]; Wang L. et al. discussed hydrodynamic hysteresis and solute transport in agglomerated heaps under irrigation, stacking, and bioleaching

**Citation:** Yin, S.; Wang, L. Editorial for Special Issue: "Current Status of Low-Grade Minerals and Mine Wastes Recovery: Reaction Mechanism, Mass Transfer, and Process Control". *Minerals* **2023**, *13*, 778. https://doi.org/10.3390/ min13060778

Received: 31 May 2023 Accepted: 6 June 2023 Published: 7 June 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

control [10]. Stepwise irrigation also plays a key role in liquid retention. Thus, Wang L. et al. deepened our understanding of the effect of stepwise irrigation on the liquid holdup and hysteresis behaviors of unsaturated ore heaps [11]. In Section 3, there are two review paper and three research papers. Yang et al. reviewed the comprehensive utilization of magnesium slag and development prospects of preparing backfilling materials [12]. Similarly, Chen et al. reviewed the art of roof contacting in cemented waste backfill technology in a metal mine [13]. Wang J. et al. focused on mine waste disposal and backfilling technology, discussing the energy dissipation, AE characteristics, and microcrack evolution of rock–backfill composite materials (RBCM) [14], and the energy dissipation mechanism and damage constitutive model of roof–CPB–floor (RCF) layered composite materials were investigated [15]. Wang L. et al. evaluated the stope stability and displacement in a subsidence area using 3Dmine–Rhino3D–FLAC3D coupling [16].

The authors who contributed to this Special Issue represent more than 10 different institutions (including Monash University Malaysia, the University of South Africa, University of Moratuwa, General Research Institute of Nonferrous Metals, Henan Polytechnic University, Central South University, University of Science and Technology Beijing, etc.) in seven different countries (China, Kazakhstan, Malaysia, Spain, Bolivia, South Africa, Sri Lanka). We thank them for their academic contributions to this Special Issue.

Last but not least, we thank the *Minerals* editorial staff for their cooperation and the invited reviewers for their valuable input.

**Funding:** This research was funded by the Program of the National Natural Science Foundation of China (52204124, 52034001); Beijing Natural Science Foundation (2232080); China National Postdoctoral Program for Innovative Talents (BX20220036), China Postdoctoral Science Foundation (2022M710356), Fundamental Research Funds for the Central Universities (FRF-IDRY-21-010, QNXM20220001); Open Project of the State Key Laboratory of Coal Mine Resources and Safety Mining (SKLCRSM22KF006); Open Project of State Key Laboratory of Safety and Health for Metal Mines (2021-JSKSSYS-01), Open Project of Key Laboratory of Green Chemical Engineering Process of Ministry of Education (GCP202108); and Fundamental Research Funds for the Central Universities (FRF-IDRY-21-010; QNXM20220001).

**Conflicts of Interest:** The authors declare no conflict of interest.

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