Removal of Pb and Zn from contaminated soil by different washing methods: the influence of reagents and ultrasound

Abstract

Pb and Zn contamination in agricultural soils has become an important issue for human health and the environment. Washing is an effective method for remediating polluted soil. Here, we compare several washing materials and methods in the treatment of Pb- and Zn-polluted farmland soil. We examined four washing reagents, hydrochloric acid, citric acid, Na2EDTA, and tartaric acid, all of which independently removed Zn at rates >65 %. Combining washing reagents markedly enhanced heavy metal removal, by using Na2EDTA and either tartaric acid or lactate in sequence: Pb and Zn removal rates improved to 84.1 and 82.1 % for Na2EDTA-tartaric acid; and to 88.3 and 89.9 % for Na2EDTA-lactate, respectively. Additionally, combining ultrasound with conventional washing methods markedly improved washing efficiency, by shortening washing duration by 96 %. We achieved similar removal rates using ultrasound for 10 min, compared with traditional mechanical vibration alone for 4 h. We concluded that treating Pb- and Zn-contaminated soil with appropriate washing reagents under optimal conditions can greatly enhance the remediation of polluted farmland soils.

Central Composite Design Optimization of Zinc Removal from Contaminated Soil, Using Citric Acid as Biodegradable Chelant

“…Zn removal efficiency increased within the time range of 30 to 120 min, before approaching a relatively constant level, indicating that soil washing with CA is a time dependent process. This observation shows a strong agreement with other studies, regarding washing time 6 , 7 , 22 , 26 . The initial rapid increases in Zn removal, followed by a levelling, may be due to the fact that the chelation process reaches equilibrium at a certain length of washing time.…”

“…Soils polluted with heavy metals can be decontaminated through a variety of methods of remediation, such as stabilization, solidification, electroremediation and phytoremediation 4 . Among the techniques of remediation, the simplicity of chemical soil washing, its low cost, short duration and high efficiency, makes it a practical option for metal removal 5 – 7 . The selection of a viable solution is a fundamental determinant of the level of efficiency of extraction in the washing process 3 , 6 , 8 .…”

Simultaneous removal of multiple heavy metals from soil by washing with citric acid and ferric chloride

“…18 In recent years, citric acid (CA), a tricarboxylic acid compound, has played an important role in removing heavy metals from soil via acid dissolution and chelation, 19 and is more readily biodegradable than EDTA. 20,21 Notably, CA leaches lower contaminants (e.g. Cd and Ni) than EDTA, except for Cr.…”

“…28 Combining washing reagents dramatically enhanced the removal efficiencies of Pb and Zn by using Na 2 EDTA and either tartaric acid or lactate. 21 Hence, searching for efficient and environmentally friendly composite washing agents is a critical step for the remediation of co-contaminated soil. 29 Batch and slurry reactor washing experiments were conducted to explore the removal of Cd, Cr, Pb and Zn from contaminated soil using 7 agents.…”

BOF steel slag as a low-cost sorbent for vanadium (V) removal from soil washing effluent

“…Vanadium can damage plant growth, reduce agricultural production 2 , and harm human health via the food chain. Soil washing is an effective remediation method that can efficiently remove heavy metals such as chromium (Cr) 3 , 4 , lead (Pb) 5 , copper (Cu) 6 , zinc (Zn) 5 – 7 , arsenic (As) 8 , and cadmium (Cd) 6 , 8 from soil. However, a large volume of washing effluent containing heavy metals is discharged in this process.…”