Study On Mutagenizing Cultivation Of Acidithiobacillus Ferrooxidans And Improved Bioleaching Of Phosphate Ore

Our country's resuorse of phosphorus is quite rich, but the rich phosphate ore is largely used out and we have to use middle or low grade phosphate ore, because it is uneven distribution and has been unreasonably exploited. The traditional processing methods are expensive and polluting for middle or low grade phosphate ore, so people are seeking for other superior methods.Bacterial leaching is cheap and unpolluting, so more and more people pay attention to it. Acidithiobacillus ferrooxidans (At.f ) is the main bacterium for leaching, because it can use oxygen from air to oxidize the reductive state of iron and sulfur, from which it gains energy and produces sulfuric acid to leach phosphorus from middle or low grade phosphate ore. Early bacterial leaching research is mainly about metal ores, but not non-metallic ores, particularly, with very little work done for phosphate ore.Therefore, the paper researches about the isolation and purification of Acidithiobacillus ferrooxidans isolated from a hot spring water sample from Guangxi, and then the use of it for experiments. The results showed that:1) For At.f strain cultivation, the best conditions in the 9 K liquid cuture medium were: initial pH 3.00, cultivation temperature 30℃, quantity of inoculation 10% (v/v);2) For Acidithiobacillus ferrooxidans leaching of low-grade phosphate ore, the purer bacteria the better it was for the leaching. Using Acidithiobacillus ferrooxidans (CH-5) used for experimental study of continuous leaching, it was found that the statistics polynomial analysis curve between rate of leaching phosphorous and time was close to Logistic model, and the formula fitting was built;3) For physical mutagenesis of Acidithiobacillus ferrooxidans for leaching low-grade phosphorate ore:â‘ the best time of the UV for the bacteria was 5-10 min;â‘¡the best time of ultrasonic mutagenesis at the frequecy of 59 kHz was about 15 min;â‘¢the best time of low temperature mutagenesis at 4℃was about 0.5-1 h;â‘£after using modified logistic model to fit the three physical mutagenesis of bacteria for leaching phosphate ore, we could find thatr (the growth rate of bacteria for leaching phosphorous) decreased butη_m (the maximum rate of bacterial leaching of phosphorous) increased, so it has not only tested the model with experiments but also proved that physical mutagenesis was good for increasing bacteria leaching of phosphorous;⑤after the orthogonal experiments, we could find that the best physical mutagenesis was ultrasonic and the time of mutagenesis was about 15 min;4) Using the bacteria strain of YB-1 cultivated under the best physical mutagenesis conditions, we could find that:â‘ quantity of inoculation 10%(v/v) and [Fe²⁺] = 9 g/L was the best;â‘¡in the experiments of the effects of reductive state sulfur on bacterial leaching of phosphorous in the same dosage of pyrite, sodium thiosulfate and sulfur, was better, especially, when the doasage of sulfur was about 0.5 g, with the highest rate of bacterial leaching of phosphorous of 62.88% in the 42^th day. Finally, we found that the time of the rapid increasing of bacteria leaching of phosphorous was in the periode of stable of bacteria. About the mechanism of bacteria leaching of phosphorous, we thought it was indirect but was based on composites—in the first, the bacteria compound contained the reductive states of sulfur, sulfide and iron to produce acid, and then using the acid on phosphorous ore for leaching. Through the use of mathematical model analysis it was found that the major driving force for the At.f bacterial leaching of low grade phosphate ore was [H⁺],[Fe²⁺] and [Fe²⁺].