# Remediation of Heavy Metal Contaminated Farmland Soil by Biodegradable Chelating Agent GLDA
## 4 Conclusions  
1. The leaching efficiency of heavy metal Pb in soil was improved by adjusting the GLDA-Na solution to reach acidity with citric acid.
2. The leaching efficiency of Pb, achieved by mixing GLDA-Na and citric acid, was greater than the sum of their respective leaching abilities. To achieve the leaching  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **GLDA-Na** & **Sodium** & **G-Sodium** & **Sodium** & **G-Sodium** & **Potassium** & **G-Potassium** \\  & **Hexametaphosphate** & **Hexametphosphate** & **Citrate** & **Citrate** & **Chloride** & **Chloride** \\ \hline Dabaoshan & 23.98 & 29.61 & 30.83 & 3.73 & 15.73 & 1.98 & 20.53 \\ Huaqiao & 33.65 & 40.39 & 44.58 & 10.47 & 28.67 & 2.63 & 34.54 \\ Tielong & 30.09 & 39.49 & 41.11 & 4.53 & 22.13 & 0.00 & 26.96 \\ Lechang & 11.40 & 34.09 & 35.70 & 0.71 & 6.70 & 0.00 & 6.81 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Leaching removal rate of Pb in the soil after the combination of GLDA-Na and different salts (%).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Full Amount (mg/kg)** & **Available Content (mg/kg)** & **pH** \\ \hline Before leaching & & & & \\ SB & 287.3 \(\pm\) 6.5 & 45.53 \(\pm\) 4.34 & 5.04 \\ TL & 146.1 \(\pm\) 17.6 & 42.877 \(\pm\) 8.765 & 6.01 \\ LT & 947.6 \(\pm\) 25.9 & & 242.4 \(\pm\) 10.4 & 7.17 \\ After leaching & & & & Reduction rate \\ SB & 160.9 \(\pm\) 8.4 & 43.97\% & 20.60 \(\pm\) 0.75 & 54.73\% & 5.00 \\ TL & 36.7 \(\pm\) 11.5 & 74.92\% & 15.11 \(\pm\) 2.35 & 64.67\% & 6.02 \\ LT & 509.5 \(\pm\) 11.3 & 46.23\% & 72.97 \(\pm\) 6.29 & 69.89\% & 6.79 \\ \hline \hline \end{tabular}
\end{table}
Table 5: The heavy metal Pb content and pH of soil before and after leaching.  
efficiency of GLDA-Na without adjusting the pH, the leaching time and the dosage of the GLDA-Na solution, adjusted by citric acid at a pH of 4, were reduced.
3. After leaching with 10 mmol/L of GLDA-4 solution for 120 min, the total Pb and available Pb in the soil decreased significantly, with decreased amplitudes of more than 44% and more than 54%, respectively.
4. The leaching rate of Pb was improved by adding sodium hexametaphosphate into GLDA-Na, but the effect of \(1+1>2\) could not be achieved.
5. The combination of GLDA and critic acid is an environmentally friendly and effective chelating agent or washing solution for the remediation of heavy metal-contaminated soils. This mixture may be a useful, effective, and environmentally friendly chelator for the remediation of heavy metal-contaminated soil.  
Conceptualization, Z.W.; Investigation, X.L. and H.R.; Supervision, Z.H.; Writing--original draft, Y.C. All authors have read and agreed to the published version of the manuscript.  
This study was supported by the Local Innovation and Entrepreneurship Team Project of the Guangdong Special Support Program, China (No. 2019 BT02L218), the Science and Technology Planning Project of Guangdong Province, China (No. 2018B030324003), and Guangdong Laboratory for the Lingnan Modern Agriculture Project (NT2021010).  
Not applicable.  
The authors declare no conflict of interest.