Upgraded Analytical Protocols in Bauxite Refining Industry Using Composite Sampling Approach to Minimize Laboratory Analysis Load

The laboratories in the bauxite processing industry are always under a heavy workload of sample collection, analysis, and compilation of the results. After size reduction from grinding mills, the samples of bauxite are collected after intervals of 3 to 4 hours. Large bauxite processing industries producing 1 million tons of pure aluminium can have three grinding mills. Thus, the total number of samples to be tested in one day reaches a figure of 18 to 24. The sample of bauxite ore coming from the grinding mill is tested for its particle size and composition. For testing the composition, the bauxite ore sample is first prepared by fusing it with X-ray flux. Then the sample is sent for X-ray fluorescence analysis. Afterwards, the crucibles are washed in ultrasonic baths to be used for the next testing. The whole procedure takes about 2 - 3 hours. With a large number of samples reaching the laboratory, the chances of error in composition analysis increase. In this study, we have used a composite sampling methodology to reduce the number of samples reaching the laboratory without compromising their validity. The results of the average composition of fifteen samples were measured against composite samples. The mean of difference was calculated. The standard deviation and paired t-test values were evaluated against predetermined critical values obtained using a two-tailed test. It was found from the results that paired test-t values were much lower than the critical values thus validating the composition attained through composite sampling. The composite sampling approach not only reduced the number of samples but also the chemicals used in the laboratory. The objective of improved analytical protocol to reduce the number of samples reaching the laboratory was successfully achieved without compromising the quality of analytical results.

Process optimization of rare earth and aluminum leaching from weathered crust elution-deposited rare earth ore with compound ammonium salts

In order to intensify the leaching process of rare earth（RE） and reduce the impurities in the leachate, ammonium chloride（NH4Cl） and ammonium nitrate（NH4NO3） were mixed as a compound leaching agent to treat the weathered crust elution-deposited RE ore. Effects of molar ratio of NH~＋_4Cl and NH_4NO_3, ammonium（NH_4） concentration, leaching agent pH and flow rate on the leaching process of RE were studied and evaluated by the chromatographic plate theory. Leaching process of the main impurity aluminium（Al） was also discussed in detail. Results showed that a higher initial ammonium concentration in a certain range could enhance the mass transfer process of RE and Al by providing a driving force to overcome the resistance of diffusion. pH almost had no effects on the mass transfer efficiency of RE and Al in the range of 4 to 8. The relationship between the flow rate and height equivalent to a theoretical plate（HETP） could fit well with the Van Deemter equation, and the flow rate at the lowest HETP was determined. The optimum conditions of column leaching for RE and Al were 1：1（molar ratio） of NH_4Cl and NH_4NO_3, 0.2 mol/L of ammonium concentration, pH 4–8 of leaching agent and 0.5 mL /min of flow rate. Under this condition, the mass transfer efficiency of RE was improved, but no change was observed for Al compared with the most widely used ammonium sulfate. Moreover, the significant difference value（around 20 mL） of retention volume at the peak concentration between RE and Al provided a possibility for their separation. It suggested the potential application of the novel compound leaching agent（NH_4Cl/NH_4NO_3）. It was found that the relative concentration of RE in the leachate could be easily obtained by monitoring the pH of leachate.