Remediation of contaminated land and solutions with binders derived from waste material.

Metal leaching behaviour was investigated in synthetically prepared soils which were contaminated with lead in the laboratory and to which ordinary Portland cement (OPC), lime, magnesia, fly ash (PFA), or ground granulated blast furnace slag (GGBFS) were added to stabilise the contaminant. The optimum amounts were determined by fly ash added gradually to contaminated soil until full reduction of leachable lead was reached. Five grams of the soil thoroughly mixed with 0.1g stabilising material was transferred into a 100ml polypropylene container to which 50ml of de-ionised (DI) water or 50 ml of 0.1M HNO[3] or 0.01M HNO[3] was added. The mixture was shaken on a flat bed shaker for 2 hours, and then filtered using a Whatman No 542 filter paper. The lead concentration in the filtrate was determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). All theses stabilizers resulted in about 99% of the added lead being retained on the filter. However, in similar experiments with 0.1 M HNO[3] effective lead retention was found only when OPC or GBFS were used where amounts retained were 90 and 95% respectively. The effect of changes in pH on lead retention was investigated using Raman Spectroscopy, X-ray Diffraction (XRD), Fourier Transformation Infrared Spectroscopy (FTIR), Raman Spectroscopy and Scanning Electron Microscopy (SEM) and X-ray photo spectroscopy (XPS) and ion chromatography.In a second series of experiments Lead contaminated solutions containing 10, 50, 100, and 500 mg/1, respectively of Pb were treated by the addition of known quantities of OPC, lime, magnesia, GGBFS or fly ash. The resulting lead-containing precipitate was collected and characterised using XRD, FTIR, Atomic emission Spectroscopy ICP-AES, SEM-EDX , Raman and XPS. Analysis of the supernatant by Inductively Coupled Plasma Spectrometry showed that about 99% of lead in solution was removed after the addition of 0.1g of OPC, lime or magnesia, PFA, or GGBFs to the 50ml of lead solution. Characterisation of the cement treated samples showed the formation of PbCO[3], PbSO[4] and PbSiO[3]. The addition of lime resulted in the formation of Pb2OCO[3], PbSiO[3], PbCO[3] and Ca(PbO[3])[2]. In the presence of magnesia, the following compounds were formed: Mg[2]Pb, PbMgV[2]O[7] and PbO[2]. Results from both IR and SEM-EDX confirmed the presence of lead in the precipitate. When deionised water or 0.1 M HNO[3] was used in the presence of GGBFS, the concentration of lead in the leachate was less than 1% of the added lead in the soil. Results from X-ray diffraction measurements on soil samples retained on the filter paper showed lead calcium silicate and a mixed compound of lead sulphate carbonate hydroxide were formed in the presence of GGBFS. These investigations show that the addition of cement, lime or magnesia, GGBFS and PFA can result in the removal of lead from the solution to form stable compounds, thus providing a potential means of clean-up of solutions contaminated with lead.In addition to the work on contamination with lead, contamination with seven other elements was also investigated: Zn, Pb, Cd, Cr, Cu, Ni, Al. The levels of the concentration of the solution were varied: 10, 50, 100 and 500 mg/1. The solidification procedures were applied with 20,000 mg/l of Pb solution on cube shape 50x50 x50mm samples that were cured for 7 days. Then tank leaching test was conducted on solidified samples together with an acid digestion test. This work was extended to the examination of the leaching behaviour of the compounds formed by subjecting lead contaminated OPC cubes (50x50x50mm), cured for 7 days, to leaching in a tank of DI water. Results showed that less than 1% of the lead had leached out within 15 days. In addition, similarly treated cubes with varying amounts of OPC replaced with fly ash or GGBFS were subjected to the leaching tank and compressive strength tests. The results of the tests showed better retention of Pb where OPC was replaced by PFA or GGBFS.