Slurry flow in mills: grate-pulp lifter discharge systems (Part 2)

Pulp lifters, also known, as pan lifters are an integral part of the majority of autogenous (AG), semi-autogenous (SAG) and grate discharge ball mills. The performance of the pulp lifters in conjunction with grate design determines the ultimate flow capacity of these mills. Although the function of the pulp lifters is simply to transport the slurry passed through the discharge grate into the discharge trunnion, their performance depends on their design as well as that of the grate and operating conditions such as mill speed and charge level. However, little or no work has been reported on the performance of grate-pulp lifter assemblies and in particular the influence of pulp lifter design on slurry transport. Ideally, the discharge rate through a grate-pulp lifter assembly should be equal to the discharge rate through at a given mill hold-up. However, the results obtained have shown that conventional pulp lifter designs cause considerable restrictions to flow resulting in reduced flow capacity. In this second of a two-part series of papers the performance of conventional pulp lifters (radial and spiral designs) is described and is based on extensive test work carried out in a I m diameter pilot SAG mill. (C) 2003 Elsevier Science Ltd. All rights reserved.

Ultrastructure of Hepatozoon boigae (Mackerras, 1961) nov comb. from brown tree snakes, Boiga irregularis, from northern Australia

Intraerythrocytic bodies identified as haemogregarine gamonts were found in 29% of 97 brown tree snakes (Boiga irregularis) examined during a haematological survey of reptiles in Australasia during 1994-1998. The morphological characteristics of the parasites were consistent with those of Haemogregarina boigae Mackerras, 1961, although the gamonts were slightly larger and lacked red caps but contained distinctive polar grey capsules. Gamonts did not distend host cells but laterally displaced their nuclei. They were contained within parasitophorous vacuoles and possessed typical apicomplexan organelles, including a conoid, polar rings, rhoptries and micronemes. Schizonts producing up to 30 merozoites were detected in endothelial cells of the lungs of 11 snakes. The absence of erythrocytic schizogony suggests the parasites belong to the genus Hepatozoon. Electron microscopy also revealed the presence of curious encapsulated organisms in degenerating erythrocytes. These stages did not possess apical complex organelles and were surrounded by thick walls containing circumferential junctions and interposed strips reminiscent of oocyst sutures.