Washing and Extraction of Metals from Contaminated Soil Constituents: Implications for Contaminated Simulated Soil and Metallurgical Wastes with Different Reagents

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.

A Comparison of Batch, Column and Heap Leaching Efficiencies for the Recovery of Heavy Metals from Artificially Contaminated Simulated Soil

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.

Zinc extraction from sewage sludge with [S,S]-EDDS

An environmentally friendly biodegradable chelant,[S,S]-ethylenediaminedisuccinic acid(EDDS),was used to separate heavy metals from sewage sludge based on chemical extraction technology.The extraction of zinc from sewage sludge with an aqueous solution of EDDS was studied under various conditions.It is found that the extraction efficiency of zinc using EDDS is equivalent to that using ethylenediaminetetraacetic acid(EDTA)at the molar ratio of chelant to total heavy metals of 1:1 over pH range of 5-9.EDDS is capable of extracting zinc from the sludge.The extraction efficiency is improved obviously and reaches a higher value within pH range from 3 to 10.The extraction efficiency maintains at about 65% when pH≥4.5 and the ratio of 10:1.By comparing the species contents of the zinc in sewage sludge before and after the extraction,it is found that the extracted zinc mainly comes from the acid soluble,reducible and oxidizable fractions.

Extraction of heavy metals from e-waste contaminated soils using EDDS

Environmental contamination due to uncontrolled e-waste recycling activities is drawing increasing attention in the world. Extraction of these metals with biodegradable chelant [S,S]-ethylenediaminedisuccinic acid （EDDS） and the factors influencing extraction efficacy were investigated in the present study. Results showed that the addition of EDDS at low pH （5.5） produced higher metal extraction than that at high pH （8.0） solution. Metal speciation analysis indicated that Cu was completely complexed with EDDS at different pH conditions with various amounts of EDDS applied. For Pb and Zn, at low EDDS dose of 0.304 mol/kg soil, they were present as Pb- and Zn-EDDS. However, at high EDDS dose of 1.26 mol/kg soil, most of Pb was bound with dissolved organic matter. Ca and A1 were found to be strong competitors for trace metals to EDDS at low application dose and low pH condition.