A flotation line for treating mineral ore particles suspended in slurry, comprising - at least three flotation units arranged in fluid connection with each other for allowing gravity-driven slurry flow between flotation units, and - a feed inlet for supplying slurry into a first flotation unit, and - a tailings outlet; wherein - each flotation unit comprises at least one flotation cell (20, 21, 22, 23), so that each flotation unit comprises at least one flotation cell equipped with a launder lip, at least one flotation cell equipped with a mixing apparatus, and at least one flotation cell equipped with a dispersed gas feeding mechanism; wherein - each flotation cell equipped with a launder lip comprises a cell inlet, a cell outlet and a concentrate outlet; wherein - at least three flotation units are configured to be uniplanar, so that bottoms of the at least three flotation units are positioned at least partially within a vertical range measured from the level of the bottom of the first flotation cell equipped with a launder lip and being larger than 150 m 3, wherein the vertical range is defined as the distance between a first line drawn at an angle of + 1° relative to horizontal and a second line (B') drawn at an angle of -1° relative to horizontal, the lines (B, B') starting from the lowest functional position of the bottom of the first flotation cell larger than 150m 3 and equipped with a launder lip, over the length of the flotation line, the length calculated by drawing a line, starting from the feed inlet and ending to the tailings outlet of the flotation line, between the cell inlets and cell outlets, through the center of the flotation cells within the flotation line, wherein the feed inlet is in the first flotation cell and the tailings outlet is in the last flotation cell (22b, 23); and wherein - the launder lip height of each uniplanar flotation unit is lower than the launder lip height of the preceding uniplanar flotation unit in the direction of the slurry flow, the launder lip height determined by the launder lip of a flotation cell of a flotation unit, wherein all of the launder lips within a flotation unit are positioned on the same vertical level, at a same position in each flotation unit of the flotation line, so that an angle of sloping (β) between a horizontal line drawn through the launder lip height of the first uniplanar flotation cell and a line drawn from a point of the first uniplanar flotation cell equipped with a launder lip and being larger than 150 m 3, and a corresponding point of the last uniplanar flotation cell equipped with a launder lip and being larger than 40 m 3, is formed; and the angle (β) is 1.5 to 10 degrees relative to horizontal, and the angle (β) being thus calculated via corresponding positions of the launder lip heights of the first uniplanar flotation cell and the last uniplanar flotation cell. - at least three flotation units arranged in fluid connection with each other for allowing gravity-driven slurry flow between flotation units, and - a feed inlet for supplying slurry into a first flotation unit, and - a tailings outlet; wherein - each flotation unit comprises at least one flotation cell (20, 21, 22, 23), so that each flotation unit comprises at least one flotation cell equipped with a launder lip, at least one flotation cell equipped with a mixing apparatus, and at least one flotation cell equipped with a dispersed gas feeding mechanism; wherein - each flotation cell equipped with a launder lip comprises a cell inlet, a cell outlet and a concentrate outlet; wherein - at least three flotation units are configured to be uniplanar, so that bottoms of the at least three flotation units are positioned at least partially within a vertical range measured from the level of the bottom of the first flotation cell equipped with a launder lip and being larger than 150 m 3, wherein the vertical range is defined as the distance between a first line drawn at an angle of + 1° relative to horizontal and a second line (B') drawn at an angle of -1° relative to horizontal, the lines (B, B') starting from the lowest functional position of the bottom of the first flotation cell larger than 150m 3 and equipped with a launder lip, over the length of the flotation line, the length calculated by drawing a line, starting from the feed inlet and ending to the tailings outlet of the flotation line, between the cell inlets and cell outlets, through the center of the flotation cells within the flotation line, wherein the feed inlet is in the first flotation cell and the tailings outlet is in the last flotation cell (22b, 23); and wherein - the launder lip height of each uniplanar flotation unit is lower than the launder lip height of the preceding uniplanar flotation unit in the direction of the slurry flow, the launder lip height determined by the launder lip of a flotation cell of a flotation unit, wherein all of the launder lips within a flotation unit are positioned on the same vertical level, at a same position in each flotation unit of the flotation line, so that an angle of sloping (β) between a horizontal line drawn through the launder lip height of the first uniplanar flotation cell and a line drawn from a point of the first uniplanar flotation cell equipped with a launder lip and being larger than 150 m 3, and a corresponding point of the last uniplanar flotation cell equipped with a launder lip and being larger than 40 m 3, is formed; and the angle (β) is 1.5 to 10 degrees relative to horizontal, and the angle (β) being thus calculated via corresponding positions of the launder lip heights of the first uniplanar flotation cell and the last uniplanar flotation cell.