Comparision of Sobek and Lawrence Methods and a Modified Technique for the Determination of Acid Neutralisation Potential of Mining Waste

Predicting the occurrence of acid mine drainage (AMD) of mining waste is important and challenging for the mining industry. Acid-base accounting tests such as the standard Sobek method and modified Lawrence method are widely used but suffer from inherent weaknesses with broad ranging and incomparable acid conditions. Various mineral samples and pyrite-mineral blends were employed for neutralisation potential test using both Sobek and Lawrence methods in this study. The influence of sample properties, test technique and associated variables on the acid neutralisation potential of the samples was studied. It was found that the Neutralisation Potential (NP) was influenced by the moles of acid per gram sample, the test method and the sample properties. The samples tested exhibited a range of acid neutralisation potentials, where all the minerals tested except pyrite and gang-B consume acid. Among the pyrite-mineral blends, it was found that the NP of blends of pyrite with minerals serpentine and chlorite are higher in the Sobek test than in the Lawrence test. This may be due to the severe experimental conditions employed in the Sobek test, resulting in more dissolution of the acid neutralising minerals. In their present form, the Sobek and Lawrence tests have many variables and subjective components. A new modified technique has been proposed to overcome these limitations. The new technique makes use of pyrite sample blends in conjunction with a set acid content per unit mass of sample. The new method approaches the problem in a systematic way which removes the subjective components from test to produce a more robust method for the reproducible determination of NP.