Development of an AG/SAG mill batch test methodology

Abstract

Autogenous grinding (AG) and semi-autogenous grinding (SAG) mills are installed in the majority of comminution circuits in the mining industry. It is known that AG/SAG mill operation varies with the properties of ore that is fed into it and therefore, it is desirable to achieve optimal mill performance by understanding how the mill responds to operating parameters. However, the process of establishing mill response relationships by conducting surveys requires significant time and resources. Therefore, a pilot scale AG/SAG mill test methodology which allows mill performance to be evaluated would lower costs, reduce material and time to gather the data required. Previous work using pilot scale AG/SAG mill tests with mills between 0.6 and 1.8m in diameter have shown that pilot scale tests can be used to successfully predict aspects of the performance of full scale mills. However, the methodologies vary significantly, mill contents often have little similarity to the industrial-scale mill’s contents and the sample quantities required can be substantial. Therefore, there is sufficient justification to support the development of an improved pilot scale test procedure. A comprehensive pilot-scale test methodology was developed to measure the 1.8m batch mill’s response to operating parameters such as ball load, mill filling and mill speed. Performance indicators such as power draw, specific production rate, mill holdup and sample size distributions were measured. The data collected from the pilot-scale tests was also compared to industrial-scale data. It was found that breakage in pilot-scale mills is dependent on operating parameters to varying degrees. An increase in ball load had the strongest effect on increasing rates of breakage. The test methodology developed also allows for the use of samples collected to predict size distributions of mill contents below 1.18 mm when less than 50% of the mill contents are balls. This result is beneficial for future test-work. The specific production rate for pilot-scale data showed a similar trend to that of industrial-scale data. In conclusion, the test methodology developed showed that the pilot-scale test was successful in simulating how AG/SAG mill performance varies with mill operating parameters.