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When treating complex co–associated low–grade scheelite with sulfur and phosphorus mixed acid co–decomposition techniques, the deterioration in tungsten resource endowment can result in significantly lower decomposition rates, with tungsten content in the decomposition residue (gypsum residue) as high as 2%. In this paper, it is envisaged that by dissolving the gypsum residue in hydrochloric acid to separate it from insoluble tungsten and then regulating the supersaturation of calcium sulfate in the hydrochloric acid solution to prepare calcium sulfate whiskers, not only can the tungsten in the decomposition residue be recovered but also the resource utilization of gypsum can be realized. The effect of Fe3+, Na+, and NH4 + on the crystallization process and morphology of calcium sulfate whiskers was investigated using atmospheric pressure acidification. When the addition amount of gypsum residue was 5.75 g/100 mL, the concentration of hydrochloric acid was 100 g/L, the stirring rate was 100 rpm, the addition amount of NaCl was 30 g/L, the temperature was reduced from 80 to 50 °C, and the L/D ratio of calcium sulfate whiskers could reach 48. The effect of mother liquor circulation on the morphology of calcium sulfate whiskers was also investigated, and the morphology of calcium sulfate whiskers was still good after 10 cycles. During the cycling process, tungsten could be enriched in the residue, and the residue tungsten content could be increased from 3 to 14%.

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This article proposes an event-triggered distributed cooperative guidance law for multiple missiles to simultaneously attack a stationary target with consideration of autopilot lag and unknown disturbances. In order to achieve a consensus on each missile’s impact time and save communication costs, the guidance law is designed on the basis of an auxiliary variable consisting of the time-to-go expression and its time derivative. Driven by the properly designed event-triggered mechanism, the information interaction among missiles performs in a need-based scheme and there is no need to continuously monitor the consensus errors between neighbor missiles. By this means, the communication burden is significantly reduced while satisfactory guidance performance is still guaranteed. The proposed guidance law can be extended to a communication failure case where one of the missiles suddenly cannot receive information from its neighbors. An integral sliding mode controller is integrated with the nominal guidance law to eliminate the adverse effects caused by unknown disturbances. Numerical simulations are carried out to illustrate the effectiveness of the proposed guidance design.

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