Lateritik Nikel Cevherlerinde Yüksek Basınçlı Kademeli Asit Liçi Uygulama Parametrelerininproses Verimi ve Sürekliliği Üzerine Etkilerinin İncelenmesi

Abstract

In the high-pressure acid leaching process of lateritic nickel ores, scaling, which occurs as a result of dissolution and precipitation mechanisms and accumulates on the surfaces of autoclave and transfer equipment, is an important problem that directly affects the working efficiency. Since scale formations are cleaned with plant shutdowns that cause working day losses, it is important to eliminate this issue that disrupts process continuity. In the HPAL process, sulfuric acid is usually fed from the first compartment of the autoclave. Within the scope of this study, the effects of incremental and variable sulfuric acid dosing into the autoclave on metal extraction recovery and process continuity due to scale formation was examined. A new design has been made by applying some modifications on the laboratory-scale autoclave in order to add desired amount of acid at certain time intervals to the autoclave operating under high pressure and temperature. Without changing the total amount of acid required for leaching, besides adding this amount to the autoclave at once, high-pressure acid leaching tests were performed by dosing acid in two and three stages and in these stages at increasing, equal and decreasing rates. The test condition (3K-E) of equal distribution in three stages across all routines provided significant improvement on both the precious metal extraction recovery and the scale formation rate compared to the standard system of single-stage acid dosage (STD) experiment. According to the three-stage equal distribution routine, the extraction recovery increased by 2.5% on nickel basis and 4.1% on cobalt basis, while at the same time impurities in the pregnant leach solution (PLS) content decreased and selectivity increased. When 3K-E is compared with the standard condition, the scale formation rate decreases by 96%. One-way analysis of variance and post-hoc tests were applied as statistical analysis methods to determine the reliability and significance level of extraction recovery and scale formation rate data between experimental groups. It was found that the results of the 3K-E experiment, which was determined as the best condition, were significantly different from the standard condition. The mechanism model controlling the reaction rate was determined by examining the leaching kinetics of these two experimental conditions. Also, the effects of temperature, acid-to-ore ratio, particle size, and agitator speed parameters were investigated in the 3K-E condition. In this context, it was determined that the parameters did not provide an improvement in the precious metal extraction, but the PLS selectivity increased a little with the fine grain size and the higher agitator speed. Neutralization and mixed hydroxide precipitate (MHP) experiments were carried out to determine the effect of the PLS obtained from the 3K-E test on the downstream process and compared with the PLS of STD condition. Removing impurities contained in higher quantities in the PLS content of the STD condition led to higher nickel and cobalt losses during the precipitation of these impurities, and a higher amount of alkaline reagent was required to reduce the impurity concentrations to the desired levels. The reagent consumption required to purify the PLS of the 3K-E experiment was 21% lower than the STD. MHP quality was considered for both conditions and experiments were designed to provide saleable product characteristics. The MHP products of the STD and 3K-E contain 38,4% Ni, 2,2% Co, and 38,9% Ni and 2,2% Co, respectively. In the 3K-E, 12% more dry-based MHP product was obtained compared to the standard condition. This improvement here is correlated with the precious metal dissolution ratio obtained as a result of incremental acid distribution.