Groundwater remediation by “in-situ” crystallization processes, Gerald Ziegenbalg Technical University Bergakademie Freiberg

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Groundwater Protection and Remediation By Induced “In-Situ” Crystallization Processes

Author            :Dr. Gerald Ziegenbalg

Designation    :Senior Scientist

Company        :Technical University Bergakademie Freiberg

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Synopsis

Groundwater pollution by migration from landfills, acid rock drainage as well as saline water intrusion are examples for problems occurring worldwide. Up to now, only few processes to “in-situ” immobilize contaminants or to direct and control the migration of polluted solutions or groundwater are known. On the other hand, many examples for changing flow conditions by crystallization or precipitation processes are found in nature. Especially the formation of slightly soluble sulphates, carbonates and hydroxides plays an important rule. The idea of the investigations which will be summarized in the paper is, to use similar processes for:

Sealing of flow paths;
Creating barriers;
Immobilization of contaminants by precipitation;
Protecting reactive surfaces by overlaying with slightly soluble minerals.

Solutions supersaturated with gypsum, barite, calcium hydroxide or calcium carbonate are brought into soil or rock formations in which a directed crystallization occurs. This process results in permeability reduction as well as immobilisation of contaminants such as heavy metals. The preparation of oversaturated solutions is possible, for example, by using precipitation inhibitors. These prevent a spontaneous precipitation during the preparation process. Temporarily stable solutions are obtained. In the presence of 250 mg/l precipitation inhibitor it is possible to synthesise solutions containing up to 40 g/l dissolved CaSO4. The resulting solutions are completely clear and have a viscosity similar to water. Decomposition and adsorption processes lead to a gradual reduction of the stability of the inhibitors. Gypsum crystallisation occurs. If this process takes place in rock or soil formations, covering of reactive mineral surfaces or sealing of the treated area is achieved. In a similar wayit is possible to initiate in-situ precipitation processes resulting in the formation of barite or calcium carbonate. Thus it becomes possible to direct groundwater movement, to encapsulate hazardous areas or to immobilize contaminants in-situ.

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