An investigation of grade variability of the Esfordi phosphate plant feed using geostatistical method

The beneficiation plants are designed and optimized for ore dressing with a permissible range of grade variation. Any fluctuation out of this range will considerably affect the concentrate quality and beneficiation recovery. This paper attempts to analyze the variability of feed grade of Esfordi phosphate plant using geostatistical method and introduces a procedure to overcome this problem. The first step was the collection of representative samples which was carried out during 960 hours on the feed stream. Based on the results obtained from this study, a periodic variation has been seen on the feed grade which might be due to ore exploitation from different mine faces and lack of any suitable blending. The high values of relative nugget effects of variograms (especially for phosphates (0.12 and 0.66 for iron and phosphate, respectively) confirm this undesirable fluctuation. In the next step, the grade homogenization of the feed was simulated using moving average technique at four time intervals (16, 24, 32 and 40 hours). By sensitivity analysis, the 32h time interval was chosen as optimized blending interval. Considering a feed rate of 140 t/h, it is necessary to blend about 4500 tons of the ore before feeding to the plant.