Washing of metal contaminated soil with EDTA and process water recycling.

We demonstrate here, in a laboratory scale experiment, the feasibility of using the base/acid pair Ca(OH)(2)/H(2)SO(4) to impose a pH gradient for EDTA recycling and, coupled with an electrochemical advanced oxidation process using a graphite anode, of recycling process water as part of a novel remediation technology for multi-metal contaminated soils. In the first batch, 60 mmol EDTA kg(-1) of soil removed 72, 27, and 71% of Pb, Zn, and Cd, respectively, from soil contaminated with 5329±685, 3401±193, and 35±6 mg kg(-1) of Pb, Zn, and Cd, respectively. In the subsequent four batches, we demonstrated that up to 88% of EDTA was recycled from each batch, with the potential to extract up to 98, 94, and 109% of Pb, Zn, and Cd, respectively, that the fresh EDTA extracted.

Novel EDTA and process water recycling method after soil washing of multi-metal contaminated soil.

The development of EDTA-based soil washing technologies is hampered by the lack of treatment methods of the spent solution, particularly when multi-metal contaminated soils have to be remediated. Extraction of Pb (5329 mg kg(-1)), Zn (3401 mg kg(-1)), Cd (35 mg kg(-1)) and As (279 mg kg(-1)) contaminated soil with 60 mmol EDTA kg(-1) of soil removed 72%, 27%, 71%, and 80% of contaminants, respectively. We demonstrate here, on a laboratory scale experiment, the feasibility of using acid precipitation with HCl and H(2)SO(4), coupled to initial alkaline Fe removal, to recover up to 88% of EDTA from a spent soil washing solution containing 11,578 mg L(-1) of EDTA and 1109, 267, 7.

Recycling of EDTA solution after soil washing of Pb, Zn, Cd and As contaminated soil.

Soil washing with EDTA is known to be an effective means of removing toxic metals from contaminated soil. A practical way of recycling of used soil washing solution remains, however, an unsolved technical problem. We demonstrate here, in a laboratory scale experiment, the feasibility of using acid precipitation to recover up to 50% of EDTA from used soil washing solution obtained after extraction of Pb (5330 mg kg(-1)), Zn (3400 mg kg(-1)), Cd (35 mg kg(-1)) and As (279 mg kg(-1)) contaminated soil.

Electrochemical EDTA recycling after soil washing of Pb, Zn and Cd contaminated soil.

Recycling of chelant decreases the cost of EDTA-based soil washing. Current methods, however, are not effective when the spent soil washing solution contains more than one contaminating metal. In this study, we applied electrochemical treatment of the washing solution obtained after EDTA extraction of Pb, Zn and Cd contaminated soil.

Electrochemical EDTA recycling with sacrificial Al anode for remediation of Pb contaminated soil.

Recycling chelant is a precondition for cost-effective EDTA-based soil remediation. Extraction with EDTA removed 67.5% of Pb from the contaminated soil and yielded washing solution with 1535 mg L(-1) Pb and 33.

Remediation of Cu-contaminated soil using chelant and EAOP.

An electrochemical advanced oxidation process (EAOP) was used for treatment of the washing solution obtained during leaching of Cu (364 +/- 2 mg kg(-1)) contaminated soil, with chelant S,S isomer of ethylenediamine disuccinate ([S,S]-EDDS). In the EAOP (constant current density 40 mA cm(-2)), a boron-doped diamond anode was used for the generation of hydroxyl radicals and oxidative decomposition of [S,S]-EDDS-metal complexes in the washing solution. The released Cu was mostly electro-deposited on the stainless-steel cathode.

Using electrocoagulation for metal and chelant separation from washing solution after EDTA leaching of Pb, Zn and Cd contaminated soil.

Electrocoagulation with an Al sacrificial anode was tested for the separation of chelant and heavy metals from a washing solution obtained after leaching Pb (3200 mg kg(-1)), Zn (1100 mg kg(-1)), and Cd (21 mg kg(-1)) contaminated soil with EDTA. In the electrochemical process, the sacrificial anode corroded to release Al(3+) which served as coagulant for precipitation of chelant and metals. A constant current density of 16-128 mAc m(-2) applied between the Al anode and the stainless-steel cathode removed up to 95% Pb, 68% Zn and 66% Cd from the soil washing solution.

EDTA leaching of Cu contaminated soil using electrochemical treatment of the washing solution.

The feasibility of a two-phase method for remediation of Cu (364+/-2 mg kg(-1)) contaminated vineyard soil was evaluated. In the first phase we used ethylenediamine tetraacetae (EDTA) for Cu leaching, while in the second phase we used an electrochemical advanced oxidation process (EAOP) for the treatment and reuse of the washing solution for soil rinsing (removal of soil-retained, chelant-mobilized Cu complexes) in a closed loop. In the EAOP, a boron-doped diamond anode was used for the generation of hydroxyl radicals and oxidative decomposition of EDTA-metal complexes at a constant current density (40 mA cm(-2)).