Magnetic separation for arsenic and metal recovery from polluted sediments within a circular economy.

Several metals and metalloids (e.g., As, Cd, Cu, Pb, Zn) are toxic at low concentrations, thus their presence in sediments can raise environmental concern. However, these elements can be of economic interest, and several techniques have been used for their recovery and some of them have been widely applied to mining or to industrial soils, but not to sediments. In this work, wet high-intensity magnetic separation (WHIMS) was applied for As, Cd, Cu, Pb and Zn recovery from polluted sediments. A composite sample of 50 kg was taken in the Avilés estuary (Asturias, North Spain) with element concentrations above the legislation limits. Element distribution was assessed using wet-sieving and ICP-MS analysis, revealing that the 125-500 µm grain-size fraction accounts for the 62 w% of the material and that element concentration in this fraction is lower than in the other grain size fractions. Subsequently, WHIMS was applied at three different voltage intensities for the 125-500 µm and <125 µm fractions, revealing excellent recovery ratios, especially for the coarser material. Furthermore, magnetic property measurements coupled to microscopy analysis revealed that the success of the technique derives from concentrating metal-enriched iron oxides particles (ferro- and para-magnetic material) in a mixture of quartz and other minerals (diamagnetic particles). These results indicate the feasibility of the magnetic separation for metal and metalloid recovery from polluted sediments, and thus offer a double benefit of coastal area restoration and valuable material recovery in the context of a circular economy.

Erosion directionality and seasonality study using the anisotropy matrix. Application in a semiarid Mediterranean climate (SE Spain).

This paper is based on the fact that some climatic variables show a preferential directionality and grant a markedly anisotropic character to the weathering system acting on rocks. The aim of this work is to quantify the anisotropic degree of the weathering system and its effects on rock erosion. For this purpose, a new methodology based on the vector analysis of directional and time-dependent parameters is proposed to quantify the annual or seasonal anisotropy of the weathering system. Results show that, on the one hand, wind-driven rain and solar radiation are the most anisotropic variables, being north and east the most intense directions for wind-driven rain and southeast for solar radiation, in the case of the San José Tower, the reference monument of this study. On the other hand, the ranking from the most to the least eroded façades of the tower are: east (maximum recession depth of 26.77 mm) > south (15.53 mm) ≈ west (13.56 mm) > north (6.37 mm). Solar radiation and indirect processes arising therefrom are the most important weathering agents in the semiarid Mediterranean climate, whilst wind-driven rain is the main erosion factor especially due to its torrential character. According to our results, weathering and erosion agents are strongly anisotropic, which emphasizes the importance of integrating the anisotropic character of the weathering system in preventive strategies against surface deterioration of monuments. In this sense, this paper advances the United Nations' 2030 Agenda for Sustainable Development.