Interrelationship of hydrology, microbial colonisation and hydrometallurgy in a simulated chalcopyrite heap leach

Includes bibliographical references (leaves 104-115).Chalcopyrite is the most abundant primary copper sulphide mineral found worldwide. As copper grades of ores available for extraction decrease, heap bioleaching is gaining interest as a potential operating alternative to traditional methods of roasting and smelting. The efficiency by which bacteria assist leaching chalcopyrite is governed by their interaction and association to the sulphide mineral in the ore. While both planktonic and mineral-associated micro-organisms contribute to the bioleaching of mineral sulphides through the oxidation of ferrous iron little information exists as to their ability to adhere and leach low grade chalcopyrite ore. This study was undertaken to determine the association of defined and mixed microbial species on a chalcopyrite concentrate and a chalcopyrite ore. At. ferrooxidans, At. caldus, At. thiooxidans and L. ferrooxidans were grown in pure culture and used to investigate the mineral-microbe association within defined experimental parameters of two experimental operations

Electrochemical Pitting And Repassivation On Icosahedral AL-CU-FE, And A Comparison With Crystalline Phases

We report the electrochemical potentials at which localized pitting and repassivation occur on icosahedral Al-Cu-Fe, and on a series of related alloys and elemental metals. The electrochemistry occurs in a buffered NaCI solution, pH 8.4. Under these conditions, pitting and repassivation appear to be controlled mainly by the chemical composition of the alloy, although the quasicrystalline phase displays an anomalous resistance to repassivation. Corrosion of this phase proceeds by dissolution of Al and Fe, leaving behind pits which are Cu-enriched

Pitting corrosion and repassivation of Al65Cu23Fe12 quasicrystals and corrosion characteristics of quasicrystalline Al65Cu23Fe12 modified by additives

The corrosion resistance of quasicrystalline Al65CU23Fe12 is important because of the unusual properties of quasicrystals. The electrochemical pitting in 0.1 M sodium chloride was studied by voltammetry to determine the value of E[Subscript pit] and E[Subscript rp] with comparisons to different phases. Metal composition appeared to be a factor in the final value of E[Subscript pit] and EP[Subscript rp]. Structure did not appear to be the overwhelming factor in the final result. The open circuit corrosion was investigated on the quasicrystalline Al65Cu23Fe12. by Tafel and polarization resistance measurements in 0.5M perchloric acid. The additives changed the electrochemical values of I[Subscript corr], indicating a higher rate of corrosion for sodium chloride. This higher rate was inhibited by the use of other sodium halides. The halide effect was investigated at a variety of pH regions. The results showed no effect from the use of additives. The quasicrystalline Al65Cu23Fe12 was connected to a stainless steel, to determine the effect of their proximity in solution. The results showed the quasicrystal corrodes first with no apparent effect on the stainless steel

Electrochemical Pitting And Repassivation On Icosahedral AL-CU-FE, And A Comparison With Crystalline Phases

We report the electrochemical potentials at which localized pitting and repassivation occur on icosahedral Al-Cu-Fe, and on a series of related alloys and elemental metals. The electrochemistry occurs in a buffered NaCI solution, pH 8.4. Under these conditions, pitting and repassivation appear to be controlled mainly by the chemical composition of the alloy, although the quasicrystalline phase displays an anomalous resistance to repassivation. Corrosion of this phase proceeds by dissolution of Al and Fe, leaving behind pits which are Cu-enriched.This article is from Quasicrystals: Proceedings of the MRS 1998 Fall Meeting 553 (1999): pp. 275—280, doi:10.1557/PROC-553-275</p

Investigating heap leaching – the effect of feed iron concentration on bioleaching performance

This paper describes an investigation into the effect of iron concentration in the leach solution on the bioleaching of a low grade copper ore, where chalcopyrite was the dominant copper sulphide. The concentration of dissolved iron is primarily controlled by pH and the relative proportion of ferric to ferrous iron, with significant jarosite precipitation occurring above pH ≈ 1.8 in a highly oxidised system. The solution pH may be increased by the dissolution of acid soluble gangue and when iron oxidation is significantly higher than sulphur oxidation. The study was approached using two experimental systems. In the former, the leach solution was recycled through an ore bed of low aspect (reactor height divided by diameter) ratio for a portion of the experiment. During the recycle phase, no acid was added to the system and acid consumption by gangue material led to a pH increase (1.6–2.2). The resulting jarosite precipitation reduced soluble iron from 2.5 g/l to less than 250 mg/l. Copper recovery decreased, but not in proportion to the decrease in iron. This was partly attributed to adsorption on, or entrainment within, the jarosites. To study the effect of reduced iron concentration on leach performance under more controlled conditions, bioleaching was performed in packed bed column reactors with feed iron concentrations ranging from 5 g/l to 200 mg/l. Observations indicated an initial decreased rate of copper liberation with reduced iron concentration in the feed. The relationship between available Fe3+ concentration and copper liberation was not proportional. However, with time, the liberation of copper became independent of iron concentration in the percolation liquor. Further, the specific rate of copper liberation was consistently below the theoretical value on a basis of ferric iron concentration. The highest values of copper liberation were reported at the lowest iron concentrations. In summary, while increased iron concentration in solution may enhance the initial rate of leaching, mineral availability appears to dominate CuFeS2 leach kinetics through the majority of the leach. Furthermore, high iron concentrations in solution aggravate jarosite formation with concomitant retention of copper in the ore bed

High prevalence of human papillomaviruses in fresh frozen breast cancer samples

While the etiology of breast cancer remains enigmatic, some recent reports have examined the role of human papillomavirus (HPV) in breast carcinogenesis. The purpose of this study was to determine the prevalence of HPV in breast cancer tissue using PCR analysis and sequencing. Fifty-four (54) fresh frozen breast cancers samples that were removed from a cohort of breast cancer patients were analyzed. Samples were tested for HPV using comprehensive PCR primers, and in situ hybridization was performed on paraffin embedded tissue sections. Findings were correlated with clinical and pathological characteristics. The HPV DNA prevalence in the breast cancer samples was 50% (27/54) with sequence analysis indicating all cases to be positive for HPV-18 type. While HPV patients were slightly younger, no correlation was noted for menopausal status or family history. HPV positive tumors were smaller with earlier T staging and demonstrated lesser nodal involvement compared to HPV negative cancers. In situ hybridization analyses proved negative. The high proportion of HPV positive breast cancers detected in this series using fresh frozen tissues cannot be dismissed, however the role of HPV in breast carcinogenesis remains unclear and may ultimately be ascertained by monitoring future breast cancer incidence amongst women vaccinated against high risk HPV types

Valproic acid combined with cytosine arabinoside in elderly patients with acute myeloid leukemia has in vitro but limited clinical activity

Elderly patients with acute myeloid leukemia (AML) have a poor prognosis. The authors examined the in vitro and clinical activity of the histone deacetylase inhibitor valproic acid (VA) combined with cytosine arabinoside (AraC) in elderly patients with AML unsuited to intensive therapy. For the in vitro studies, primary AML cells from 11 patients were treated with AraC and VA and analyzed for apoptosis, cytostatic effects, differentiation and acetyl histone H3 induction. VA (alone and with AraC) enhanced apoptosis and induced acetyl histone H3. VA inhibited cell proliferation. For the clinical trial, 15 patients were treated with VA and subcutaneous AraC and assessed for toxicity and response. No complete or partial remissions were achieved. In concusion, VA has in vitro activity against AML and has additional activity with AraC. However, in this study, this combination demonstrated limited clinical activity in elderly patients with AML

Haplotype analysis of two recurrent CDKN2A mutations in 10 melanoma families : evidence for common founders and independent mutations

Germ-line mutations in CDKN2A have been shown to predispose to cutaneous malignant melanoma. We have identified 2 new melanoma kindreds which carry a duplication of a 24bp repeat present in the 5' region of CDKN2A previously identified in melanoma families from Australia and the United States. This mutation has now been reported in 5 melanoma families from 3 continents: Europe, North America, and Australasia. The M53I mutation in exon 2 of CDKN2A has also been documented in 5 melanoma families from Australia and North America. The aim of this study was to determine whether the occurrence of the mutations in these families from geographically diverse populations represented mutation hotspots within CDKN2A or were due to common ancestors. Haplotypes of 11 microsatellite markers flanking CDKN2A were constructed in 5 families carrying the M53I mutation and 5 families carrying the 24bp duplication. There were some differences in the segregating haplotypes due primarily to recombinations and mutations within the short tandem-repeat markers; however, the data provide evidence to indicate that there were at least 3 independent 24bp duplication events and possibly only 1 original M53I mutation. This is the first study to date which indicates common founders in melanoma families from different continents