By Jonathan Landay DERGACHI, Ukraine (Reuters) – Ukrainian forces destroyed parts of a Russian armoured column as it tried to cross a river in the Donbas region, video from Ukraine’s military showed on Friday, as the Ukrainian defence minister predicted many weeks of grinding fighting ahead. Ukrainian forces have driven Russia from the second-largest Ukrainian city of Kharkiv in their fastest advance since Kremlin troops pulled away from Kyiv and the northeast over a month ago to focus their offensive on the Donbas region bordering Russia. The city, which had been under fierce bombardment, has…