In-Situ Coal Pit Lake Treatment of Acidity When Sulfate Concentrations Are Low

Abstract

Pit lakes (abandoned flooded mine pits) represent a potentially valuable resource to mining companies, the environment and community, if appropriate water quality can be achieved. However, the water is often of low pH with high dissolved metal concentrations. In Western Australia coal pit lakes are acidic (pH 3-5) but with low concentrations of sulfate and metals. Low sulfate concentrations prevent microbial sulfate reduction from reducing acidity in these lakes. However, stimulation of primary production and associated alkalinity generating processes may provide a cost effective and sustainable solution to the acidity problems. A field-scale experiment (with control) involving the treatment of in-situ macrocosms (~600 m 3) in a small southwest , Western Australian coal mine lake with municipal mulch and phosphorus additions to enhance primary production was undertaken between June 2003 and June 2004. One macrocosm was treated with P additions, another with mulch, a third with mulch and P, and the untreated lake formed the control. Physico-chemical and algal (chlorophyll a) sampling of the macrocosms and lake occurred at monthly intervals. The decomposition of mulch reduced nitrogen concentrations in the macrocosms to very low levels and necessitated supplementation with urea fertilizer. Phosphorus concentrations dropped rapidly after addition as it became bound to iron, organic matter and sediment. Although there was virtually no difference between treatments and control for most physico-chemical parameters measured (including pH), a PCA of the data showed that the addition of mulch sent the macrocosms on a different trajectory to the control. This difference was reflected in observations of increased abundance and diversity of biofilms and macroinvertebrates within the treated macrocosms. In conclusion, the addition of mulch and phosphorus alone was not sufficient to increase the pH of Collie mine lakes, although it does provide a number of benefits for biota in the water. We therefore recommend that liming be used to increase pH, followed by organic matter and nutrient additions to stimulate primary production.

Formation of biogenic sulphides in the water column of an acidic pit lake: biogeochemical controls and effects on trace metal dynamics

“…Although preliminary tests at laboratory scale showed promising results (Frömmichen et al 2003;Fyson et al 2006), the application of these saprobization and eutrophication technologies to pit lakes has proven difficult. Examples of this complexity are those of Berkeley pit lake, Butte (Montana, US) (Geller and Schultze, 2013) or lake Ewington (Australia) (Lund et al 2006). A major problem seems to be the preservation of reducing conditions to prevent the reoxidation of biogenic sulphides (Geller et al 2009;Koschorreck et al 2002Koschorreck et al ), (2007 which is especially complicated in holomictic lakes (Brugam and Stahl 2000).…”

Processes at the Sediment Water Interface after Addition of Organic Matter and Lime to an Acid Mine Pit Lake Mesocosm

“…However, after some weeks, the water quality inside the enclosures returned to the initial state. Enclosures (600 m 3 ) in an Australian pit lake, treated with mulch and/or phosphorus, only resulted in minor changes to water quality (17). A meromictic mine lake, treated with lime, exhibited an increase in pH which led to the precipitation of metals.…”