This paper shows the effect of three different leaching processes and 4 different leaching agents on the extraction of five metals of interest from an artificially contaminated simulated soil (SS). For the first time, it is shown that these processes and extractants could be compared directly, as the soil was a constant variable. The interest of this study is that the recovery of metals that are of importance in the circular economy, have been demonstrated from an unusual resource, soil. Metal reserves are constantly decreasing worldwide and alternative resources becoming topical. Urban mining of contaminated land and/or waste sites, therefore, becomes an attractive choice for metal extraction/recovery. This study has shown that metal extraction of up to 50% efficiency could be achieved. Furthermore, EDTA proved to be the best overall extractant when used in batch leaching processes. However, different metals showed preferential recoveries with specific processes and extractants. Therefore the results suggest that the design of a contaminant-specific leaching process performed in a sequential manner could not only leach the metals, but also achieve reasonable separation of the metals.

Introduction: Air pollution in cosmopolitan cities is increasingly becoming unprecedented with attendant effects on human and biophysical attributes. Materials and methods: The study was carried out at Federal University of Technology (FUTO) and environs in the southeastern Nigeria. Some ambient air quality parameters (CO, CO2, NO2, CH4 and noise) were sampled and. measured at seven unique locations (OR, ER, FR, EJ, IM, FM and FJ) with multi sampler devices, using air differential technique during the morning, midday and evening periods. Results: The average pollutant results show increased concentrations at the different locations when compared to Occupational Safety and Health Administration (OSHA) than Federal Ministry of Environment (FMEnv) thresholds (FMEnv>CO2<OSHA; FMEnv>NO2<OSHA; FMEnv>CH4<OSHA). However, concentrations of CO and Noise in FR and FJ were relatively higher than concentrations observed in other locations (CO: FR [6.4 mg/m3] and FJ [4.2 mg/m3]; Noise: FR [96.8 dB] and FJ [95.7 mg/m3]) respectively. Conclusion: The significant increase could be attributed to continuous vehicular emissions and presence of make-shift activities in these locations. However, predictive model suggests that given the meteorological conditions and perceived anthropogenic activities over time, OSHA threshold could be evidently compromised.

The extraction and recovery of metals from contaminated soil has become inevitable considering the increasing premium placed on environmental and human health protection as well as predicted shortfalls in primary metal production. In this study, metal extraction from two industrially contaminated soils (Copsa-mica [Rb-So] and Campina [Ro-PH]) were considered for process (column and heap) leaching configuration using different selected chelating substances; ethylene diamine tetraacetic acid [EDTA], ethylene diamine disuccinic acid [EDDS], acetylacetone [Hacac] and citric acid [CA]. The result confirms optimal recovery of EDTA column-induced-Rb-So over chelant-heap induced configuration and was adopted for economic prediction using two possible (60% and 100%) recycled scenarios. The 100% recycled scenario resulted in a viable economic process sufficient enough to offset clean-up cost. Metal separation and recovery from M-EDTA complex could be facilitated with the use of H2S gas precipitated in hydrogen flame combustion. The process economics predicted offered a probable prospect for metal separation from washing liquor.

Leaching behaviour of heavy metals (HMs) from simulated soil (SS), prepared according to standard guidelines, as well as its constituents (quartz sand (QS), bentonite clay (BC), and peat moss (PM)) were investigated. The study focused on a batch process with the aim of comparing the leaching potentials and metals solubilisation of ethylene diamine tetraacetic acid (EDTA), ethylene diamine disuccinic acid (EDDS), acetylacetone (Hacac), citric acid (CA), and tartaric acid (TA) for sustainable metal extraction purposes after a maximum leaching time of 60 min. The HMs concentrations with which the constituents were spiked with was such that reflected a contaminated site. The recovery potentials of both the SS and its constituents were found to vary for single metal (SM) and multi-metal (MM) systems. EDTA was the most efficient (on average 31% and 33% for SM and MM) and TA the least efficient (on average of 2% and 3% for SM and MM) extractant. For Hacac, preferential recovery for Cu and Ni were significant when compared to the other metals, while, metal recovery by EDDS in SS was lower than could be expected. The leaching trend for the targeted metals was studied using conventional leaching models.