Direct and reverse flotation technique for high-magnesium low-grade phosphorus ore coarse grains

The invention relates to a direct and reverse flotation technique for high-magnesium low-grade phosphorus ore coarse grains. The technique comprises the following steps: crushing and grinding high-magnesium low-grade phosphorus ores; transferring into a flotation machine stirring tank and adding water for mixing slurry; keeping the temperature of the ore slurry at 10-30 DEG C, and then respectively adding regulator sodium silicate and inorganic base into the ore slurry; adding a direct flotation collecting agent for mixing the slurry; adding water for performing direct flotation system operation; transferring a direct flotation foam product into a reverse flotation stirring tank, respectively adding the regulator sodium silicate and reverse flotation mixing collecting agent into the reverse flotation stirring tank, and mixing the slurry without adding fresh water; adding fresh water and performing the reverse flotation system operation; discharging and stacking the foam products which are reverse flotation tailings, wherein the products in the tank are low-magnesium phosphorus ore concentrates; concentrating, filtering and drying, thereby acquiring the end products of concentrates. According to the technique, the last magnesium content of the concentrates is reduced and the quality of the concentrates is increased; the process is simple; the energy consumption for ore grinding is low; the dosage of agents is less; the separation effect is good; the discharging rate of magnesium is high; the water quality of concentrate and tailing is improved.