Optimal refuge chamber position in underground mines based on tree network.

Safety is a critical concern in underground mining. Operations should be designed according to a vision of zero accident and fatality. A refuge chamber is a station where worker lives are maintained throughout an emergency until they are saved. Given that workers perform their duties in different areas of underground, the number of refuge chambers and their locations are of paramount importance as workers must be able to access them rapidly. Furthermore, the task of refuge chamber localization needs to consider the fact that the number of workers in a different area and the structural characteristics and stability conditions of these areas will not be identical. This paper aims to determine the optimal locations of the refuge chambers in the underground network considered as a tree. Initially, a formula quantifying the importance of each worksite is developed. Then, two main strategies are presented as feasible localization solutions: A recursive solution to the 'Absolute Weighted P-centre Problem' and a spiral approach to the 'Total Covering problem'. The functionalities of the proposed approaches are demonstrated by case studies. Results show that the proposed methods can find viable locations for refuge chambers while fulfilling varied maximum safety distances of each working area.

Process optimization for acidic leaching of rare earth elements (REE) from waste electrical and electronic equipment (WEEE).

E-waste (EW) from discarded electrical and electronic devices is a potential source of rare earth elements (REEs) that might be recovered from urban and industrial wastes. REEs are essential raw materials for emerging and high technologies. China currently dominates global REE production with a proportion of 97%. To increase the independence of REE supply and eliminate the environmental impacts related to REE mining, methods for an efficient REE recovery from secondary sources like EW are needed. In this work, we examine improvements in pre-treatment and acidic leaching processes to recover REEs and other valuable metals. EW was crushed and ground prior to the sieving. The materials obtained were then subjected to acid leaching. The parameters used to optimize the conditions for leaching were as follows: acid type (HCl, HNO3, and aqua regia), particle size, and waste-to-acid ratio. The maximum leaching efficiency was obtained from the ground, sieved, and undersized part of e-waste by using HCl with a W:A of 12.5 mg/mL. The total REE concentration was 435 mg/kg. Several treatment scenarios are identified with promise for improving REE recovery at full scale in EW recovery plants and thereby advancing goals for a sustainable, circular economy.

Risk assessment of trace metals in an extreme environment sediment: shallow, hypersaline, alkaline, and industrial Lake Acigöl, Denizli, Turkey.

The major and trace element component of 48 recent sediment samples in three distinct intervals (0-10, 10-20, and 20-30 cm) from Lake Acigöl is described to present the current contamination levels and grift structure of detrital and evaporate mineral patterns of these sediments in this extreme saline environment. The spatial and vertical concentrations of major oxides were not uniform in the each subsurface interval. However, similar spatial distribution patterns were observed for some major element couples, due mainly to the detrital and evaporate origin of these elements. A sequential extraction procedure including five distinct steps was also performed to determine the different bonds of trace elements in the < 60-µ particulate size of recent sediments. Eleven trace elements (Ni, Fe, Cd, Pb, Cu, Zn, As, Co, Cr, Al and Mn) in nine surface and subsurface sediment samples were analyzed with chemical partitioning procedures to determine the trace element percentage loads in these different sequential extraction phases. The obtained accuracy values via comparison of the bulk trace metal loads with the total loads of five extraction steps were satisfying for the Ni, Fe, Cd, Zn, and Co. While, bulk analysis results of the Cu, Ni, and V elements have good correlation with total organic matter, organic fraction of sequential extraction characterized by Cu, As, Cd, and Pb. Shallow Lake Acigöl sediment is characteristic with two different redox layer a) oxic upper level sediments, where trace metals are mobilized, b) reduced subsurface level, where the trace metals are precipitated.