Action time effect of lime on its depressive ability for pyrite

Two sample groups of bulk concentrates consisting mainly of pyrite andchalcopyrite from Daye and Chenghchao Mines in Hubei Province of China were used to investigate theeffect of the action time of lime on its depressive ability for pyrite. The experimental resultsconducted with different samples and collectors showed that the action time between lime and pyritemarkedly influences the depressive ability of lime. The depressive ability of lime increased withthe action time increasing. It was also proved that the depressive results obtained at a large limedosage after a shorter action time are similar to those obtained at a small lime dosage after alonger action time. The increase of depressive ability of lime after a longer action time is becausethat there are different mechanisms in different action time. The composition on the surface ofpyrite acted for different time with lime was studied by using ESCA (Electron Spectroscopic ChemicalAnalysis). The results showed that iron hydroxide and calcium sulphate formed on the pyrite surfaceat the presence of lime in the pulp but the amounts of iron hydroxide and calcium sulphate weredifferent at different action time. At the beginning action time the compound formed on the pyritesurface was mainly calcium sulphate and almost no iron hydroxide formed; but with the action timeincreasing, iron hydroxide formed. The longer the action time, the more iron hydroxide and the lesscalcium sulphate formed. It was considered that the stronger depressive ability of lime after alonger action time is because more iron hydroxide forms on the pyrite surface.

A modified predictive control strategy of three-phase grid-connected converters with optimized action time sequence

Due to the excellent dynamic performance,the Finite Control Set Model Predictive Control has been widely used in various types of converters.However,when Finite Control Set Model Predictive Control is adopted,the switching frequency of converters varies significantly with system operating conditions.Consequently,constant-frequency predictive control strategy has been proposed.Two active voltage vectors and a zero voltage vector are selected within each sampling period.The action time sequence is then calculated.Due to the unsymmetrical distribution of current variation rates around zero,the calculated value of the voltage-vector action time will turn up negative.According to common sense,the voltage-vector action time is greater than or equal to zero.The action time is normally forced to zero whenever a negative value is predicted,resulting in the control failure and performance deterioration.To solve this problem,this paper proposes modified strategy.The modified strategy examines the action time calculated out.When negative action time comes out,the modified strategy reselects the active voltage vector accordingly,instead of forcing the action time to be zero.Optimized action time sequence is further determined by minimizing the cost function.The effectiveness of the modified strategy is clearly verified by experimental tests,and analytical remarks are all founded in practical results.