Pellet hardness was determined with manually operated compression pellet tester “Pellet Hardness Tester“, AMANDUS KAHL GmbH & Co. KG, Germany, by measuring the force of the first fracture of individual pellets. Twenty pellets of approximately equal length, from each batch were tested. The results of the measurements are expressed as Kahl hardness.
Bulk density of ground and pelleted AP was measured with a bulk density tester (Tonindustrie, West und Goslar, Germany).