The response of tropical wetlands to the geochemical conditions of discharged water from nickel laterite mines

Amin, Radjali (2017). The response of tropical wetlands to the geochemical conditions of discharged water from nickel laterite mines PhD Thesis, Sustainable Minerals Institute, The University of Queensland. doi:10.14264/uql.2017.461

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Author Amin, Radjali
Thesis Title The response of tropical wetlands to the geochemical conditions of discharged water from nickel laterite mines
School, Centre or Institute Sustainable Minerals Institute
Institution The University of Queensland
DOI 10.14264/uql.2017.461
Publication date 2017-03-27
Thesis type PhD Thesis
Supervisor Mansour Edraki
David Mulligan
Craig Sheridan
Total pages 332
Total colour pages 96
Total black and white pages 236
Language eng
Subjects 0302 Inorganic Chemistry
0602 Ecology
Formatted abstract
In the nickel laterite mines of tropical areas, chromium, particularly hexavalent chromium which is toxic to biota, can be released to aquatic environment through surface runoff in soluble and suspended form. Constructed wetlands could be a remediation option for chromium in mine water. However, most previous studies about metals removal from mine water using constructed wetlands are conducted in non-tropical areas which may not be directly applicable to tropical areas, where nickel laterite mines are predominantly located. Macrophyte species selection, potential substrate matrixes, and the structure of a constructed wetland, are the main design criteria that need to be taken into account in constructing a wetland with high removal efficiency.

The aim of this study is to identify the essential wetland conditions that determine the success of chromium removal from surface runoff waters at two nickel laterite mines, in a tropical area of Indonesia.

A combination of field survey and laboratory experiments were conducted to investigate the efficiency of constructed wetlands in removing chromium from mine water. At the nickel laterite mines of Obi Island, Indonesia, the concentration of chromium was high in mine water but it was reduced to levels below the detection limit at the centre of a natural tropical wetland receiving contaminated surface water. The sediment ponds which were constructed to control the total suspended solids also successfully remove hexavalent chromium from the mine water.

The presence of macrophytes, the organic-rich sediment of the natural wetland, and the long residence time, enhance the efficiency of chromium removal from water. Five native macrophytes were identified in the natural wetland. Two of these species, Lepironia articulata and Machaerina rubiginosa, used in the initial mesocosm experiments showed a high potential for use in a constructed wetland. The initial on-site experiments showed these macrophytes were metal excluders and their root system played a significant role in chromium removal efficiency. It was also evident that the addition of organic materials increased the removal efficiency of the mesocosms. However, the addition of organic materials also accelerated the release of chromium from the natural mine sediment, which was used as mesocosm substrate.

These macrophytes were propagated hydroponically in the glasshouse and showed their roles in removing hexavalent chromium from the artificial mine water. Another experiment involving two types of organic matters, i.e. cow manure and coconut husks, in removing hexavalent chromium from water has shown that each organic material has its own characteristics and sorption capacities in responding to the geochemistry of the artificial mine water containing hexavalent chromium.

Based on the initial experiments, a wetland mesocosm was constructed to investigate the optimum structure and the operating system for removing hexavalent chromium from aqueous solution, and to develop an optimum removal rate. The mesocosm, using a locally sourced substrate and selected macrophytes, was constructed applying different types of water flow structures to measure the area removal rate constants. The system removed hexavalent chromium from the artificial mine water by predominantly reducing hexavalent chromium to trivalent chromium. An important zone of the mesocosm was the sediment/water interface where hexavalent chromium was reduced to trivalent chromium and precipitated. However, turbulence and diffused oxygen from the roots of the macrophytes, could re-oxidise the chromium to hexavalent chromium. The deeper points in the sediment with lower redox potentials could reduce the hexavalent chromium and precipitate the trivalent chromium onto the surface of the particles. Increasing the number of macrophyte species from two to three species, and increasing the size of vegetated area from 25% to 40%, did not increase the removal efficiency of the wetland mesocosm.

It was found that the free water surface (FWS) wetland system had lower area removal rate constants than the hybrid flow (a combination of subsurface and surface flow) system. For the calculation of the removal rate constant of the mesocosm, the Peclet (Sheridan, Glasser, & Hildebrandt, 2014) was better than first order equation, because the value of the variants of Peclet equation was smaller than the first order equation, meaning that the Peclet equation was more accurate than the first order equation.

Although the hybrid system was better than the FWS system, it is not recommended to be applied on site due to potential clogging of the constructed wetland. A constructed wetland in Obi Island should function as a polishing pond to maintain a high level of efficiency of chromium removal from the mine waste water.
Keyword Constructed wetlands
Nickel laterite
Chromium - Environmental aspects
Additional Notes 3, 12, 17-18 landscape, 36-38, 59,60, 64,65, 67, 69-72, 74,75, 81, 93, 97, 99-102, 105-107, 109-111, 113, 119-121, 127, 131-135, 143, 144, 148, 151, 154, 156, 157, 159, 165, 166, 169, 170, 175-177, 180, 184-187, 190-197, 199-201, 203-207, 209, 214-216, 218, 219, 222 color landscape, 226 color landscape, 228 color landscape, 230 color landscape, 231, 233, 236,237, 240, 245, 246, 253, 256, 258, 302 color landscape, 303 color landscape.

Document type: Thesis
Collections: UQ Theses (RHD) - Official
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Created: Tue, 21 Mar 2017, 00:16:26 EST by Radjali Amin on behalf of Learning and Research Services (UQ Library)