Abstract
Flocculants play a major role during thickening of slurries in thickeners. However, residual flocculants have detrimental effects in the downstream processes. In a Platinum group minerals (PGMs) concentration circuit, water circulated from Chrome removal plant (CRP) thickener, reduces recoveries in the flotation process. The impact of the residual flocculant on the flotation on UG2 ore was investigated. Feeds from the Primary rougher tails and CRP into the flotation circuits were characterized using X-Ray Fluorescence (XRF) and X-Ray diffraction (XRD) in order to determine chemical and mineralogical composition. The Cloudy and CRP water sample were characterized against dissolved flocculant using UV-spectrometry by comparing the chemical absorbance at 200-800nm and 220-800nm wavelength. The settling test of process water (combined CRP and Cloudy water) and Fresh water against flocculant were done using a cylinder. The samples of feed slurry that contained Cloudy water from the primary rougher tail and feed slurry that contained CRP water from CRP were collected separately in every two hours for four times and taken for hot float to investigate effect of residual flocculant on 4E (Pt, Pd, Rh and Au) recovery, grade and their mass pulls. The 26 samples of feed slurry with CRP water and Cloudy water were collected separately on 13 consecutive days for each stream and floated. The flotation process was optimized using design of experiment (DoE) approach, using central composite design (CCD) method.
The results revealed that the feed from primary rougher tails, the mineralogical is that of UG-2 ore which consists mainly of chromite (75%), orthopyroxene (18%) and the rest are minor. The feed has high %mass of chrome (30.1%) with low %mass of 4E present (1.2%). The CRP feed contained chromite (40%), orthopyroxene (30%) and other minor minerals. The feed contained low chrome (9.5%) and slightly higher percent of 4E (1.6%).
The UV-spectrometry results showed that, there was some chemical absorbance of dissolved flocculant in both CRP and Cloudy water. However, CRP water had higher residual flocculant concentration (0.22Abs) than Cloudy water(15Abs). The settling test results indicated interface level of flocculant dropping more significantly from 350mm to 50mm in 300 seconds followed by process water mixture from 350mm to 230mm in 300 seconds and fresh water remained on 350mm without showing any changes in 300 seconds.
The flotation results revealed that there is a higher 4E recovery when floating using Cloudy water (70.1-76.59%) compared to CRP water (54-62%). However, the 4E grade obtained when floating using CRP water (9.8-14g/t) was higher than that of Cloudy water (8.3-8.9g/t. Higher
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mass pulls were observed when using Cloudy water (9.8-10.67%) compared to CRP water (7.37-8.2%). The optimum condition of flotation using Cloudy water was at mass pull of 5.02% with frother dosage of 1.3g/t and depressant dosage of 32.07g/t, producing a concentrate with 4E recovery of 83.09% and grade of 19.88g/t whilst the CRP water were 4.890% Mass pull with frother dosage of 1.4g/t and depressant dosage of 19g/t, producing a concentrate with 4E recovery of 85.090% and grade of 20.89g/t.
Key words: UG2 ore, residual flocculant, flotation performance, 4E recovery, Platinum Group Metals