Recycling of lead-contaminated EDTA wastewater.
Ethylene diaminetetraacetic acid (EDTA) is one of the chelating agents used in the soil washing process for the decontamination of lead-contaminated soil. Lead-EDTA complexes in the wastewater from the soil washing process must be removed before the wastewater can be safely discharged. This study outlines a method to recycle Pb-EDTA wastewater by substituting the Pb complexed with EDTA with Fe(III) ions at low pH, followed by precipitation of Pb ions with phosphate or sulfate ions. Fe(III) ions complexed with EDTA were then precipitated at high pH using sodium hydroxide. The resulting solution (Fe-precipitated solution) was tested on three lead-contaminated soils. The Fe-precipitated EDTA solution was found to have similar extraction capabilities as fresh EDTA solution. Experimental results showed that the recycled EDTA solution may be recycled several times without losing its extractive power. Recycled EDTA wastewater with phosphate precipitation was found to be slightly more effective than recycled EDTA solution using sulfate precipitation. The recycling procedure may be applied to wastewater generated during soil washing of lead-contaminated soil, resulting in a reduction in wastewater generated and savings in the amount of EDTA used.
Recovery of copper and chelating agents from sludge extracting solutions
Removal of extraction solution containing chelated copper from printed circuit board industry sludge by cementation on powdered iron was studied. This work applied the recovery and extraction of ethylene diamine tetraacetate (EDTA) and diethylene triamine pentaacetate (DTPA) as remediation agents and metal precipitated from printed circuit board sludge extracting solutions. The recovery of copper by cementation process using powdered iron was dependent on the Fe:Cu molar ratio. Results of the experiments showed that recovery efficiencies were typical of those of a Fe:Cu molar ratio as high as 8:1 for each sludge sample. The differences of recovery efficiencies may be due to competition for active sites on the surface of the powdered iron. Copper deposits on the surface almost always occur in the form of the copper metal that are well distributed, with purified copper powder being observed in characterization with scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The recycled extract containing EDTA or DTPA was used to chelate supplementary fresh copper-containing sludge. Extraction efficiencies of copper by using Fe-precipitated EDTA or DTPA from previous cementation were higher than sequential application of the Fe-EDTA or Fe-DTPA solution. Similar copper extraction efficiencies using both pristine and reused extract containing chelants validates the enduring chelating capability of EDTA and DTPA and suggests further opportunities to employ recycled chelant to reduce its usage. This work confirmed the feasibility of copper removal from sludge chelated wastewater by cementation and subsequent recycling of chelant extraction.
Frequency distributions of the mixing height over an urban area from SODAR data
The height of the mixing-layer (MLH) is an important parameter in the assessment of the dilution of primarily emitted or secondarily formed air pollutants in the atmospheric boundary-layer. A continuous measurement of MLH is possible only by remote sensing. Here, 17 months of SODAR data have been analysed automatically to derive the MLH over the city of Hannover in Northern Germany. In contrast to earlier studies the MLH has been determined from vertical profiles of the acoustic backscatter intensity and from the variance of the vertical velocity component. The results are presented in form of monthly frequency distributions and mean daily courses of MLH. These statistical evaluations of MLH show a clear annual course and interannual variability. The study shows the possibility to derive meaningful climatological information from long-term SODAR measurements for air quality issues.