Nonsulfide flotation technology and plant practice

Book ChapterThere are hundreds of nonsulfide mineral flotation plants throughout the United States, and most have a plant design that depends upon the specific ore characteristics and the market specifications for their product. There is no common thread of technology between the design and processing of different nonsulfide minerals, or even between processing minerals of the same kind. Although most nonsulfide processing plants utilize flotation, other mineral separation techniques are often necessary to yield a marketable product. Typical beneficiation techniques used in conjunction with flotation include gravity separation, magnetic separation and chemical leaching. Sometimes several different flotation systems are used in the same processing plant, such as the flotation of mica, quartz and feldspar from pegmatite ores. Usually there is a primary material produced at a nonsulfide processing plant with other mineral products sold as by-product material. Often the economics of a facility is dependent upon the by-products and sometimes the by-products become the most profitable commodity produced at a plant. The stone, sand and gravel industry is the exception and is not included in this chapter. This nonsulfide mining industry is huge, exceeding all the metals industry and fuel industry tonnage combined. These mining operations do not beneficiate their material by flotation nor do they normally use any other mineral separation process. This industry mines a one-component deposit that only requires removal of fines and clays to produce a saleable product

Adsorption of mono- and multivalent cat- and anions on DNA molecules

Adsorption of monovalent and multivalent cat- and anions on a deoxyribose nucleic acid (DNA) molecule from a salt solution is investigated by computer simulation. The ions are modelled as charged hard spheres, the DNA molecule as a point charge pattern following the double-helical phosphate strands. The geometrical shape of the DNA molecules is modelled on different levels ranging from a simple cylindrical shape to structured models which include the major and minor grooves between the phosphate strands. The densities of the ions adsorbed on the phosphate strands, in the major and in the minor grooves are calculated. First, we find that the adsorption pattern on the DNA surface depends strongly on its geometrical shape: counterions adsorb preferentially along the phosphate strands for a cylindrical model shape, but in the minor groove for a geometrically structured model. Second, we find that an addition of monovalent salt ions results in an increase of the charge density in the minor groove while the total charge density of ions adsorbed in the major groove stays unchanged. The adsorbed ion densities are highly structured along the minor groove while they are almost smeared along the major groove. Furthermore, for a fixed amount of added salt, the major groove cationic charge is independent on the counterion valency. For increasing salt concentration the major groove is neutralized while the total charge adsorbed in the minor groove is constant. DNA overcharging is detected for multivalent salt. Simulations for a larger ion radii, which mimic the effect of the ion hydration, indicate an increased adsorbtion of cations in the major groove.Comment: 34 pages with 14 figure

Unexpected Role for Helicobacter pylori DNA Polymerase I As a Source of Genetic Variability

Helicobacter pylori, a human pathogen infecting about half of the world population, is characterised by its large intraspecies variability. Its genome plasticity has been invoked as the basis for its high adaptation capacity. Consistent with its small genome, H. pylori possesses only two bona fide DNA polymerases, Pol I and the replicative Pol III, lacking homologues of translesion synthesis DNA polymerases. Bacterial DNA polymerases I are implicated both in normal DNA replication and in DNA repair. We report that H. pylori DNA Pol I 5′- 3′ exonuclease domain is essential for viability, probably through its involvement in DNA replication. We show here that, despite the fact that it also plays crucial roles in DNA repair, Pol I contributes to genomic instability. Indeed, strains defective in the DNA polymerase activity of the protein, although sensitive to genotoxic agents, display reduced mutation frequencies. Conversely, overexpression of Pol I leads to a hypermutator phenotype. Although the purified protein displays an intrinsic fidelity during replication of undamaged DNA, it lacks a proofreading activity, allowing it to efficiently elongate mismatched primers and perform mutagenic translesion synthesis. In agreement with this finding, we show that the spontaneous mutator phenotype of a strain deficient in the removal of oxidised pyrimidines from the genome is in part dependent on the presence of an active DNA Pol I. This study provides evidence for an unexpected role of DNA polymerase I in generating genomic plasticity

A new class of errant DNA polymerases provides candidates for somatic hypermutation.

The mechanism of somatic hypermutation of the immunoglobulin genes remains a mystery after nearly 30 years of intensive research in the field. While many clues to the process have been discovered in terms of the genetic elements required in the immunoglobulin genes, the key enzymatic players that mediate the introduction of mutations into the variable region are unknown. The recent wave of newly discovered eukaryotic DNA polymerases have given a fresh supply of potential candidates and a renewed vigour in the search for the elusive mutator factor governing affinity maturation. In this paper, we discuss the relevant genetic and biochemical evidence known to date regarding both somatic hypermutation and the new DNA polymerases and address how the two fields can be brought together to identify the strongest candidates for further study. In particular we discuss evidence for the in vitro biochemical misincorporation properties of human Rad30B/Pol iota and how it compares to the in vivo somatic hypermutation spectra