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In order to integrate necessary interdisciplinary complexity, sustainability, defined targets and endpoints for reclamation progress, the objective of this research is to advance reclamation knowledge on (i) international scale and (ii) national scale, taking Nigeria as an example. On the international scale (i), a systematic reclamation threshold scale for assessing, evaluating, documenting, and monitoring reclamation progress was developed. The threshold stages begin from the initial state I0 down to degraded state D0 (depending on the type of mining). Reclamation starts with soil reconstruction R-2 up to revegetation R-1 (red zones) to reach minimum threshold R0 (amber zone). Beyond R0 are the green zones R1, R2, and R3 representing soil/abiotic condition, biological and improved threshold respectively. Adaptation of the threshold model to degraded ecosystems in national and international laws is recommended. On the national scale with Nigeria (ii), endowed with over 34 solid minerals and abundant crude oil, findings show that almost all mine sites are below the minimum threshold scale R0. The sites are adversely affected by Artisanal and Small Scale Mining (ASM), whereby, contamination and soil lithology disturbances are the state-of-the-art discussions. However, bioremediation (phytoremediation) is the most feasible remediation technique. Therefore, for the crude oil contaminated sites, this study highlights typical cogitation for large in-situ implementation and potential species for remediation. For the mineral resources, gold mining was the typical example. As a practical approach, experimental areas on an abandoned mining site (Site 1), an active mining site (Site 2) and an undisturbed vegetation site (Control) in southwestern Nigeria were mapped out to represent its mining and farming activities. On the sites, (a) the impacts of the ASM activities on the floristic association were assessed. (b) the potential of 2D Electrical Resistivity Tomography (ERT) was explored to characterize the horizontal and vertical landscape homogeneity of the mine sites, and lastly, (c) the study identified native high-accumulating plants growing on the sites that can be employed for phytoremediation. Thus, the results show that (a) the floristic association of the mine sites have been stressed and disturbed. (b) the resistivity structure of the sites shows that ASM has greatly impaired the lithological status of the sites. (c) out of the 9 considered species, Crinum jagus has the highest accumulation factor of 8.71, 37.47, 1.08 and 29.38 for Pb, Cd, Fe and Cu respectively. It is a recommendable novel plant in the tropics. However, future studies must verify its hyperaccumulator potentials, identify other high accumulating species and develop effective approaches and policies to curb ASM activities and enhance remediation in Nigeria.
Detection and behavior of iron-cyanide complexes in soils of a former Manufactured Gas Plant site
(2014)
Soils and groundwater on sites of the former Manufactured Gas Plants (MGPs) are contaminated with various complex iron-cyanides (Fe-CN). The aim of this thesis was to evaluate a new method for the CN detection and to investigate the stability and retardation of Fe-CN complexes in soils. This study seeks for enhancing the efficiency of phytoremediation as a proper approach to decontaminate Fe-CN complexes and thus tries to make a contribution to environmental protection.
Feasibility of Field Portable Near Infrared (FP NIR) Spectrometry to determine CN concentrations in soil was evaluated in order to develop a rapid and non-destructive in-situ method. The study revealed that FP NIR could be a reliable device for detecting CN concentrations >2400 mg kg−1 in the field and >1750 mg kg−1 after sample preparation in the laboratory, however the limits of detection are too high to replace the traditional methods.
The applicability of neutral solution extraction to determine the water soluble CN fraction and the stability of Prussian Blue under saturated and unsaturated water conditions was studied in a column and batch experiments. Study revealed continuous solubility of Prussian Blue, in acidic and slightly alkaline MGP soils. Dissolution of ferric ferrocyanide under circum-neutral pH and oxic water conditions was proposed to be a function of time, where the released amount is dependent on the soil pH and total CN content.
Modeling the long-term release of Fe-CN complexes from the MGP soils revealed two-phase-process. The fast released phase was attributed to the transport process of readily dissolved hexacyanoferrats that is taking place in the liquid phase combined with desorption of CN bound to heterogeneous surfaces that are in direct contact with aqueous phase (outer-sphere complexation). The CN release rates increased with increasing pH, decreased with low initial CN concentration and were retarded by the increase in OM content.
The retardation of Fe-CN in soil was investigated in batch and column experiments. Experiments revealed that the excess of the available iron, which induced the formation of the Prussian Blue colloids despite the circum-neutral pH, was a very important factor in decreasing the CN concentration. Additionally, despite the chemical factors influencing the potential reaction with manganese oxides, the physical factors like pore size distribution, variation in the grain size etc. can reduce the CN concentration due to mechanical retention of the vertical colloidal ferric ferrocyanide movement. This study proposes colloidal vertical transport of the solid Fr-CN complexes as a potential alternative process influencing the CN mobility in the circum-neutral pH and under the excess of available iron conditions.
The results presented in this thesis revealed limitations of the FP, but advancing the sample pretreatment procedures can improve the feasibility of the spectrometer in detecting CN signal. Long-term extraction with the distilled water provides reliable assessment of the potential environmental hazard due to continuous dissolution of the solid Fe-CN complexes. Inconsistency of the Prussian Blue stability reported in the literature to the one obtained in this study imply usage of the CN contaminated MGP soils, instead of synthetic solutions, to advance the knowledge concerning the solid Fe-CN dissolution behavior. Furthermore, in the non-acidic soils the CN solubility might be influenced by the equilibrium with manganese Fe-CN mineral.