Investigating impact of pulp density on flotation performance

Abstract

The Red Dog Mine, located in northwest Alaska, is one of the world's largest zinc/lead mines. The processing mill feed consists of a blend of ores from two different pits, namely, the Aqqaluk pit and the Qanaiyaq pit respectively. The mill circuit consists of grinding and multiple flotation circuits which separate zinc and lead minerals from their gangue contents depending on the interfacial tension between hydrophilic/hydrophobic mineral surfaces and their environment. The flotation circuit feed is characterized by high percent solids (~ 50%). Percent solids can potentially have a significant effect on the grade/recovery curve. Thus, it is very common that low-density slurries give better flotation response (high grades), particularly in flotation systems containing a significant amount of liberated hydrophilic unwanted mineral particles. Moreover, the blended feed is metallurgically complex and weathered, thus adversely affecting the performance of the mill. This project investigated the effects of pulp density on Red Dog flotation circuit performance and develop strategies to maximize recovery at 50% solids. Higher solids content increases the rheology of the slurry thereby causing turbulence and froth instability. To study the impacts of slurry density on flotation kinetics, a series of experiments were conducted by varying various operating and process parameters and assessing circuit optimization strategies. Initial batch tests performed on cyclone overflow samples showed that residence time, rotor revolution per minutes (RPM), and slurry density are important factors affecting flotation performance. Lower slurry densities usually lead to better kinetics. However, in the case of the initial tests, results indicated that slurry density has a minimal effect if residence time is increased. It was shown that yields as high as 73% with Lead (Pb) recovery values of 86.20% is possible even at 60% solids concentration by increasing the residence time. If the slurry is sufficiently diluted then higher rotor speeds combined with higher residence time would provide higher yields and recoveries. Initial results indicate that at lower RPM ranges, adequate residence time and higher slurry densities lead to better bubble loading and froth stability. Lead (Pb) and Zinc (Zn) recovery values of 89.42% and 80.33% were achieved at 20% solids and 1800 RPM rotor speed. Future test work includes investigation of froth stability and pulp phase kinetics, statistically, and designed programs to optimize flotation performance in high-density slurries. Several parameters including dosage, and type of collector, pH, the dosage of frother, dosage of depressant, the dosage of activator, type of grinding media, particle size, and bubble size were controlled in the optimization tests. The optimized condition was obtained for both galena, and sphalerite at different solid%. The locked cycle tests were designed based on the Red Dog flotation circuit. At the optimized condition, the grade, and recovery for solid 30% improved by around 0.5%. The optimized condition had a further impact on the flotation performance at a higher solid%. By increasing the solid%, the grade was improved by 1.84%, and 2.24% at galena concentrate for 40%, and 50%, respectively, compared to the normal condition. Recovery was improved for both solid% by less than 1%. The optimized condition increased Zn grade at the flotation circuit by 1%, and recovery by 4% for 40% of solid. In addition, the optimized condition increased grade at the flotation circuit by 5%, and recovery by 4% for 50% of solid.