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Nickel mobilization in a sandy aquifer in response to groundwater acidification
Published in Poul L. Bjerg, Peter Engesgaard, Thomas D. Krom, Groundwater 2000, 2020
C. Kjøller, F. Larsen, D. Postma
The acidification of the groundwater at the Grindsted field site can be recognized as a sharp downward migrating front. Above the acidification front, pH values between 4.4 and 4.6 are observed along with dissolved aluminum concentrations in the order of 0.2-0.3 mM (Fig. 1). Below the front, the pH ranges from 5.8 to 6.5 and aluminum concentrations have decreased to below 0.01 mM. Equilibrium calculations using PHREEQC suggest that pH and aluminum concentrations are mainly constrained by equilibrium with a gibbsite-type mineral. However, a minor part of the pH buffering can also be accounted for by silicate weathering.
Biogenic Silica Indicator of Paleoproductivity in Lacustrine Sediments of Svalbard, Arctic
Published in Neloy Khare, Climate Change in the Arctic, 2022
Shabnam Choudhary, G. N. Nayak, Neloy Khare
Atmospheric CO2 plays an essential role in silicate weathering. During silicate weathering, dissolved CO2 is consumed and dissolved silicate (DSi), i.e., ortho-silicic acid (H4SiO4), is released from the crystalline structure of silicate minerals. For example, in the weathering of anorthite (over kaolinite) to gibbsite, DSi is produced, and CO2 is consumed (Stumm and Morgan 1974).
Health risk assessment and source identification of groundwater arsenic contamination using agglomerative hierarchical cluster analysis in selected sites from upper Eastern parts of Punjab province, Pakistan
Published in Human and Ecological Risk Assessment: An International Journal, 2021
Nisbah Mushtaq, Noshin Masood, Junaid Ali Khattak, Ishtiaque Hussain, Qasim Khan, Abida Farooqi
Agglomerative Hierarchical cluster (AHC) analysis was employed on the given dataset to group together the main factors favoring the release of As into groundwater. Using the method of minimum variance, factors were separated from each other using Euclidean distance as the dissimilarity criterion. The resulting dendrogram divided the dataset into three main clusters as shown in Figure 6. AHC grouped As, pH, depth, NO3−, Mg2 +and Ca2+ in one single class (Group 1) highlighting the importance of their interdependence on each other. The value of pH in groundwater is an important factor that controls the overall negative charge on colloids or clay minerals, hereby, controlling the adsorption or desorption of many different oxy-anions from their surfaces (Li et al. 2020). The process of As contamination by desorption from mineral oxide surfaces at high pH conditions is termed as alkali desorption and is one of the main mechanism controlling As release under natural conditions (Smedley and Kinniburgh 2002; Nicolli et al. 2012). Both silicate weathering and cation-exchange raise the pH of the groundwater as evidenced by the resultant alkaline nature (pH = 7.0–9.3) of current studied groundwater samples. Furthermore, moderate correlation of As with pH (r = 0.2) (Figure 7) imply that alkali desorption might be to some extent controlling As release into groundwater. This control of pH on As release is already well established and documented by Farooqi, Masuda, and Firdous (2007) and Mushtaq et al. (2018) in adjacent areas of study site. Calcium has been reported to compete with As for adsorption on mineral surfaces (Xie et al. 2008), however, the poor to weakly negative correlation of As with Ca2+ (r = 0.02) and Mg2+ (r = −0.11) (Table S1) suggest cation exchange capacity to be not high enough to cause desorption of As through this pathway.