Industrial plant of leathers milling treatment (1; 50; 100; 150) with improved environmental impact including: - a milling drum (2; 152) comprising a hollow body (3; 153), suitable to be rotated around a symmetry axis through motorization means and inside which the leathers to be treated are received; - a closed circuit (4; 54; 104; 154), operatively connected with said hollow body (3; 153) of said milling drum (2; 152) for the input and output in and from said hollow body ( 3; 153) of air for the treatment of said leathers; - a dust collector (5; 55; 105) for cleaning said air from particles, impurities or dusts released by said leathers, arranged outside said hollow body (3; 153) of said milling drum (2; 152) and downstream said hollow body (3; 153) following, as reference direction, the path of said air inside said closed circuit (4; 54; 104; 154); - forced ventilation means (6; 56; 106), arranged downstream said dust collector (5; 55; 105) following, as reference direction, the path of said air inside said closed circuit (4; 54; 104; 154); - at least one exchange valve (7; 57; 107) arranged downstream said forced ventilation means (6; 56; 156) following, as reference direction, the path of said air inside said closed circuit (4; 54; 104; 154); - one or more electric resistances (8; 58; 108; 158), arranged downstream said exchange valve (7; 57; 107), following, as reference direction, the path of said air inside said closed circuit (4; 54; 104; 154), characterized in that it comprises additional air purification means (9; 59; 109; 159), arranged outside said hollow body (3; 153) of said milling drum (2; 152), in line on said closed circuit (4; 54; 104; 154) and externally downstream said dust collector (5; 55; 105), operatively connected to actuation means suitable to operate said additional purification means (9; 59; 109; 159) to at least reduce the unhealthy smell accompanying said air coming from said milling drum (2; 152). - a milling drum (2; 152) comprising a hollow body (3; 153), suitable to be rotated around a symmetry axis through motorization means and inside which the leathers to be treated are received; - a closed circuit (4; 54; 104; 154), operatively connected with said hollow body (3; 153) of said milling drum (2; 152) for the input and output in and from said hollow body ( 3; 153) of air for the treatment of said leathers; - a dust collector (5; 55; 105) for cleaning said air from particles, impurities or dusts released by said leathers, arranged outside said hollow body (3; 153) of said milling drum (2; 152) and downstream said hollow body (3; 153) following, as reference direction, the path of said air inside said closed circuit (4; 54; 104; 154); - forced ventilation means (6; 56; 106), arranged downstream said dust collector (5; 55; 105) following, as reference direction, the path of said air inside said closed circuit (4; 54; 104; 154); - at least one exchange valve (7; 57; 107) arranged downstream said forced ventilation means (6; 56; 156) following, as reference direction, the path of said air inside said closed circuit (4; 54; 104; 154); - one or more electric resistances (8; 58; 108; 158), arranged downstream said exchange valve (7; 57; 107), following, as reference direction, the path of said air inside said closed circuit (4; 54; 104; 154),