A flotation line for treating mineral ore particles suspended in slurry, comprising a rougher part with at least one rougher flotation cell (111a, 111b) for the separation of slurry into underflow and overflow with the help of flotation gas, the overflow from a rougher flotation cell (111a, 111b) arranged to flow directly into a cleaner flotation line; and a scavenger part with at least two scavenger flotation cells (112a, 112b) for the separation of slurry into underflow and overflow with the help of flotation gas, wherein - overflow from a scavenger flotation cell (112a, 112b) is arranged to flow back into a rougher flotation cell (111a, 111b) of the rougher part of the flotation line, or into a regrinding step and then into a cleaner flotation line; - underflow of each preceding flotation cell of the flotation line is directed to a subsequent flotation cell of the flotation line as infeed until a last flotation cell of the flotation line, the last flotation cell being a scavenger flotation cell the underflow of which is directed out of the line as tailings, - at least 75 % of the flotation cells in the flotation line comprise a mechanical agitator comprising a rotor, a stator, and a system for introducing flotation gas into the flotation cell; and - the flotation cells of the flotation line are connected in series and arranged in fluid communication; characterized in that at least one of the flotation cells comprising a mechanical agitator comprises, in addition to the mechanical agitator, a microbubble generator for introducing microbubbles into the slurry, underflow from a previous flotation cell is arranged to be led into a subsequent flotation cell by gravity, in that the microbubble generator comprises a slurry recirculation system, and wherein the microbubble generator is arranged to receive slurry from a bottom of a flotation cell via an outlet, and to return the slurry comprising microbubbles back into the flotation cell via at least one return inlet arranged above, in the vertical direction of the flotation cell, the outlet. - overflow from a scavenger flotation cell (112a, 112b) is arranged to flow back into a rougher flotation cell (111a, 111b) of the rougher part of the flotation line, or into a regrinding step and then into a cleaner flotation line; - underflow of each preceding flotation cell of the flotation line is directed to a subsequent flotation cell of the flotation line as infeed until a last flotation cell of the flotation line, the last flotation cell being a scavenger flotation cell the underflow of which is directed out of the line as tailings, - at least 75 % of the flotation cells in the flotation line comprise a mechanical agitator comprising a rotor, a stator, and a system for introducing flotation gas into the flotation cell; and - the flotation cells of the flotation line are connected in series and arranged in fluid communication; characterized in that at least one of the flotation cells comprising a mechanical agitator comprises, in addition to the mechanical agitator, a microbubble generator for introducing microbubbles into the slurry, underflow from a previous flotation cell is arranged to be led into a subsequent flotation cell by gravity, in that the microbubble generator comprises a slurry recirculation system, and wherein the microbubble generator is arranged to receive slurry from a bottom of a flotation cell via an outlet, and to return the slurry comprising microbubbles back into the flotation cell via at least one return inlet arranged above, in the vertical direction of the flotation cell, the outlet.