Abstract: The grade of bismuth in the tailings of a copper concentrator is 3.94%. Bismuth mainly exists in the form of natural bismuth， followed by that in chalcopyrite and galena. According to the characteristics of samples， the flotation process was adopted to recover bismuth from copper tailings. In order to further optimize the flotation indexes， a mixture model was established with the amount of ethylthionitrogen and butyl xanthate as independent variables and bismuth recovery as dependent variables to determine the optimal ratio of ethylthionitrogen and butyl xanthate firstly. On this basis， the central composite design was used to design the response surface， taking grinding fineness， sodium sulfide dosage， sodium carbonate dosage and combined collector dosage as independent variables and bismuth recovery as dependent variables， a four factors and five levels mathematical model was established. Then， a roughing flotation test was carried out according to the model designed test， and the test results were analyzed by variance analysis to verify the reliability of the model. Finally， according to the optimal flotation conditions determined by response surface method， the closed-circuit flotation test of "one roughing-three cleaning-two scavenging" was carried out. The results show that: ① under the conditions of grinding fineness of -0.074 mm accounting for 85%， calcium oxide dosage of 4 kg/t， sodium sulfide dosage of 150 g/t， sodium carbonate dosage of 900 g/t， No.25 dithiophosphate collector dosage of 100 g/t and total combined collector dosage of 200 g/t， the optimal ratio of combined collector was diethyldithiocarbamate with butyl xanthate for 4∶1. ② The P value of the variance analysis model is less than 0.05， and the grinding fineness and sodium sulfide dosage had significant influence on the recovery of bismuth. The optimum rough flotation conditions determined by response surface method were grinding fineness of -0.074 mm accounting for 86%， sodium sulfide dosage of 140 g/t， sodium carbonate dosage of 750 g/t， combined collector dosage of 250 g/t， the maximum predictive recovery rate of bismuth was 83.77% and the actual recovery rate of bismuth was 83.85%. ③ According to the optimum flotation conditions determined by response surface method， Bismuth concentrate with a bismuth grade of 24.47% and bismuth recovery rate of 79.25% was obtained by using the closed-circuit flotation test of “one roughing-three cleaning-two scavenging”， the recovery was nearly 2 percentage higher than that of the original closed-circuit flotation process. The results show that the mixture design and response surface method can be used to optimize the process parameters of bismuth flotation， and has high reliability.

Key words: bismuth metal, flotation, mixture design, response surface method