Influence of high pulp density and its mode of addition on copper and zinc bioextraction from polymetallic concentrate: LSTR study

摘要

The present study was conducted to check the influence of increasing pulp density, mode of pulp addition and comparison of batch and fed batch semi continuous bioleaching process in 5 1 LSTR with a working volume of 3 1 for polymetallic concentrate. 5 to 30% (w/v) pulp densities was taken in batch experiments. In this experiment, highest copper and zinc extraction rates of 0.58 and 6.62 g.l~(-1).d~(-1) respectively were obtained with 15% (w/v) pulp density. The metal extraction rates were reduced to 0.36 and 5.10 g.l~(-1).d~(-1) for copper and zinc when 25% (w/v) pulp density was used. Higher pulp density upto 30% (w/v) was investigated with a different mode of pulp addition. When the pulp was added in smaller fractions, the extraction rate was found to be enhanced irrespective of the total pulp added during the process. The maximum of 0.7 and 6.8 g.l~(-1).d~(-1) of copper and zinc were extracted when 20% (w/v) pulp was added in four equal fractions. These extraction rates were maintained even for 25% and 30% (w/v) of the pulp added in the fractions. The beneficial effect of the fractionation of pulp additions induced to run semi continuous repeated fed batch process which was studied with 50% (v/v) leachate replacement using 20% (w/v) pulp density with two different designs. In both the designs, 3 vessel cascade system was used to provide six days of residence time. The design of sequential serial transfers of the material was found to be superior than reshuffling of transfers. In design 1, the metal extractions ranged between 60.5 to 73.5% for copper and between 63.1 to 92.1% for zinc which was between 59.4 to 66.16% and 44.7 to 52.1% respectively for design 2. In the 1st design, considerable variations in metal extractions were recorded amongst the reactor vessels, which was not noted in second design. The total acid consumption was less in design 1 than design 2 and in batch process. In all the experiments, leaching profiles viz. pH, redox potential, soluble ferrous and acid consumption were studied. The investigations show the possibility of bioleaching process with 30% (w/v) pulp density of polymetallic concentrate using fractional pulp addition mode. The semi continuous sequential serial transfer fed batch process with high pulp density was found to be the method of choice. The finding could be further improved with continuous feed supply in the selected design.