Influences of key factors on manganese release from soil of a reservoir shore

In the summertime, the manganese pollution in moderately deep lakes and reservoirs caused by thermal stratification processes has been a serious problem. To mitigate the issue, understanding the key factors that control manganese releases from reservoir soils is a critical step. To this end, batch experiments and the response surface methodology (RSM) analysis were conducted in this study to investigate the release of Mndiss and Mn(III) (0.45 μm filterable) from soil samples collected along a reservoir shore under different combined effects of pH, dissolved oxygen (DO), temperature, and dissolved organic carbon (DOC). According to the three-dimensional (3-D) response surfaces plotted from the mathematical model, the highest concentrations of Mndiss and Mn(III) released from the studied soils were achieved when the release process was carried out at 30.0 °C using a citric acid solution (10.8 mg/L) of pH 6.0 with the DO concentration of 0.0 mg/L. It was found that pH was the most significant factor affecting the release of Mndiss and Mn(III) among the four factors. The combined effect of pH and DOC was also very significant to stimulate Mn(III) releases. In addition, both Mndiss and Mn(III) followed the same release principle under the coupled effects of the four factors. A close agreement between experimental and predicted values from the developed models was found.