Analysis of Changes in Hydration Products During Solidification/Stabilization Process of Heavy Metals in the Presence of Magnesium Potassium Phosphate Cement

Abstract To study the changes in hydration products over time during the solidification/stabilization process of magnesium potassium phosphate cementing material (MKPC) and to reveal the solidification mechanism of heavy metal elements in MKPC, methods, such as scanning electron microscope-energy spectrum (SEM-EDS), X ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) etc., were used to analyze the composition and microstructure of MKPC solidified body products with different production time, which are further adulterated with heavy metals, such as Zn, Cu, Ni, Cd and Cr, as well as changes in phases of hydration products. The results showed that the preliminary, intermediate and the final hydration products were MgHPO 4 ×7H 2 O, Mg 2 KH(PO 4 ) 2 ×15H 2 O and MgKPO 4 ×6H 2 O(MKP), respectively on day 7, day 15, day 30, day 45 and day 60 after the curing of the solidified body, which was adulterated with heavy metals. Based on the analysis of the result of Cu 2+ solidification test through FTIR, Mg 2+ was replaced by Cu 2+ in MKPC hydration products to generate CuKPO 4 , and the structure of the original hydration products did not have a crystal lattice change. The scanning electron microscope image (SEM) showed that cracks and harmful voids in the MKPC solidified body decreased gradually during the curing period between day 7 and day 60, and the effect of heavy metal solidification was strengthened. Based on energy spectrum analysis, heavy metal ions existing in the hydration products and MKPC could be used to solidify heavy metals. It was thus concluded that MKPC could solidify heavy metals, primarily due to the fact that heavy metals are capable of replacing Mg 2+ . Also, they participate in a variety of chemical reactions to generate heavy metal phosphate, which could react with heavy metal ions and precipitate them. Such sediments cement and the cemented body can seal partial heavy metal ions, and the combined actions could further solidify and stabilize heavy metals

Effects of elevated atmospheric CO2 and nitrogen fertilization on nitrogen cycling in experimental riparian wetlands

Studies on the relationship between plant nitrogen content and soil nitrogen reduction under elevated CO2 conditions and with different nitrogen additions in wetland ecosystems are lacking. This study was meant to assess the effects of elevated CO2 concentrations and inorganic nitrogen additions on soil and plant nitrogen cycling. A cultured riparian wetland, alligator weeds, and two duplicated open top chambers (OTCs) with ambient (380 μmol/mol) and elevated (700 μmol/mol) CO2 concentrations at low (4 mg/L) and high (6 mg/L) nitrogen fertilization levels were used. The total plant biomass increased by 30.77% and 31.37% at low and high nitrogen fertilization levels, respectively, under elevated CO2 conditions. Plant nitrogen content decreased by 6.54% and 8.86% at low and high nitrogen fertilization levels, respectively. The coefficient of determination (R2) of soil nitrogen contents ranged from 0.81 to 0.96. Under elevated CO2 conditions, plants utilized the assimilated inorganic nitrogen (from the soil) for growth and other internal physiological transformations, which might explain the reduction in plant nitrogen content. A reduction in soil dissolved inorganic nitrogen (DIN) under elevated CO2 conditions might have also caused the reduction in plant nitrogen content. Reduced plant and soil nitrogen contents are to be expected due to the potential exhaustive use of inorganic nitrogen by soil microorganisms even before it can be made available to the soil and plants. The results from this study provide important information to help policy makers make informed decisions on sustainable management of wetlands. Larger-scale field work is recommended in future research. Keywords: Elevated CO2 concentration, Invasive species, Plant growth, Climate change, Inorganic nitrogen, Nitrogen cyclin

Identification of Trichloroethene in Groundwater Using Trees

Several tonnes of useful chemicals are produced every year for use in households, agriculture production and industries. However, these chemicals move from their original production or application sites through the air, surface or groundwater or soils and are deposited in unintended places. The resultant contamination of these matrices and the subsequent effects on living organisms, have become a major concern for researchers and policy makers. This study aimed at using literature to briefly review the role of plants in identifying trichloroethene contamination in groundwater. It was found that plants, through direct contact with the soil and such processes as advective uptake, translocation, diffusion and particle deposition are able to incorporate most of these contaminants into their tissues and store them in leaves, branches and trunks. The entire process of removing TCE by this method has thus been found to be inexpensive, easy to undertake and has been shown to be environmentally friendly. It may therefore be an effective way for the identification and analysis of this contaminant