A flotation line for treating mineral ore particles suspended in slurry, comprising a rougher part with at least one rougher flotation cell for the separation of slurry into underflow and overflow with the help of flotation gas, the overflow from a rougher flotation cell arranged to flow directly into a cleaner flotation line; and a scavenger part with at least two scavenger flotation cells for the separation of slurry into underflow and overflow with the help of flotation gas, wherein - overflow from a scavenger flotation cell is arranged to flow back into a rougher flotation cell 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 is arranged to flow back into a rougher flotation cell 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 . <EOS>