Bioleaching of realgar nanoparticles using the extremophilic bacterium Acidithiobacillus ferrooxidans DLC-5

BACKGROUND: This paper presents micro- and nano-fabrication techniques for leachable realgar using the extremophilic bacterium Acidithiobacillus ferrooxidans (A. ferrooxidans) DLC-5. RESULTS: Realgar nanoparticles of size ranging from 120 nm to 200 nm were successfully prepared using the highenergy ball mill instrument. A. ferrooxidans DLC-5 was then used to bioleach the particles. The arsenic concentration in the bioleaching system was found to be increased significantly when compared with that in the sterile control. Furthermore, in the comparison with the bioleaching of raw realgar, nanoparticles could achieve the same effect with only one fifth of the consumption. CONCLUSION: Emphasis was placed on improving the dissolvability of arsenic because of the great potential of leachable realgar drug delivery in both laboratory and industrial settings

Arsenic tolerance and bioleaching from realgar based on response surface methodology by Acidithiobacillus ferrooxidans isolated from Wudalianchi volcanic lake, northeast China

Background: Traditional methods of obtaining arsenic have disadvantages such as high cost and high energy consumption. Realgar is one of the most abundant arsenic sulphide minerals and usually treated as waste in industry. The aim of the present study was to screen an arsenic tolerant bacterium used for bioleaching arsenic from realgar. Results: An acidophilic iron-oxidizing bacterium BYQ-12 was isolated from Wudalianchi volcanic lake in northeast China. BYQ-12 was a motile, rod-shaped gram-negative bacterium with an optimum growth at 30°C and pH 2.5. 16S rDNA phylogeny showed that BYQ-12 was a new strain of Acidithiobacillus ferrooxidans. The inhibitory concentrations (ICs) of arsenite and arsenate were 32 and 64 mM, respectively. A significant second-order model was established using a Box­Behnken design of response surface methodology (BBD-RSM) and it estimated that a maximum arsenic bioleaching rate (73.97%) could be obtained when the pulp concentration, pH and initial ferrous ion concentration were set at optimized values of 0.95% w/v, 1.74 and 3.68 g/L, respectively. SEM, EDS and XRD analyses also revealed that there was direct bioleaching besides indirect electrochemical leaching in the arsenic bioleaching system. Conclusion: From this work we were successful in isolating an acidophilic, arsenic tolerant ferrous iron-oxidizing bacterium. The BBD-RSM analysis showed that maximum arsenic bioleaching rate obtained under optimum conditions, and the most effective factor for arsenic leaching was initial ferrous ion concentration. These revealed that BYQ-12 could be used for bioleaching of arsenic from arsenical minerals.

Arsenic content in Portland cement: A literature review.

Portland cement (PC) is a hydraulic binding material widely used in the building industry. The main interest in its use in dentistry is focused on a possible alternative to mineral trioxide aggregate (MTA) because PC is less expensive and is widely available. In dentistry, PC has been used in dental procedures such as pulpotomy, pulp capping, repair of root perforation and root-end filling. The purpose of this article is review the dental literature about the PC, its composition with special attention to arsenic content, properties, and application in dentistry. A bibliographic research was performed in Bireme, PubMed, LILACS and Scopus data bases looking for national and international studies about the PC composition, properties and clinical use. It was observed that PC has favorable biological properties very similar to those of MTA. The PC has shown good cell proliferation induction with formation of a monolayer cell, satisfactory inflammatory response, inhibitory effect of prostaglandin and antimicrobial effect. Studies have shown that PC is not cytotoxic, stimulates the apposition of reparative dentin and permits cellular attachment and growth. Regarding arsenic presence, its levels and release are low. PC has physical, chemical and biological properties similar to MTA. Arsenic levels and release are low, therefore, unable to cause toxic effects.

In-vitro relationship between protein-binding and free drug concentrations of a water-soluble selective beta-adrenoreceptor antagonist (atenolol) and its interaction with arsenic.

The degree of binding of a drug to plasma proteins has a marked effect on its distribution, elimination, and pharmacological effect since only the unbound fraction is available for distribution into extra-vascular space. The protein-binding of atenolol was measured by equilibrium dialysis in the bovine serum albumin (BSA). Free atenolol concentration was increased due to addition of arsenic which reduced the binding of the compounds to BSA. During concurrent administration, arsenic displaced atenolol from its high-affinity binding Site I, and free concentration of atenolol increased from 4.286 +/- 0.629% and 5.953 +/- 0.605% to 82.153 +/- 1.924% and 85.486 +/- 1.158% in absence and presence of Site I probe respectively. Thus, it can be suggested that arsenic displaced atenolol from its binding site resulting in an increase of the free atenolol concentration in plasma.

Estudio del pH y presencia de metales pesados de un trióxido mineral / Study of the pH and the presence of heavy metals from a mineral trioxide

El propósito del presente trabajo fue comparar in vitro la capacidad de alcalinización por inmersión en agua destilada de dos trióxidos minerales y analizar su polvo para determinar la presencia de metales pesados como arsénico y cromo en su composición. Se prepararon tres muestras para cada grupo. Se registró el pH del agua destilada, se sumergió cada muestra y se volvió a realizar la medición inmediatamente a la hora, a las tres horas y a los 7 días, mateniéndolñas en una estufa a 37ºC. Se determinó la presencia de arsénico por espectrometría de absorción atómica con generación de hidruros y de cromo por espectrometría de absorción atómica con horno de grafito. Los resultados del pH fueron evaluados en función del tiempo. El pH inicial de CPM fue 10,14 y a los 7 días 10,94, en tanto que para ProRoot MTA fue 8,98 y 11,87 respectivamente, determinando que el incremento del pH de CPM y MTA fue diferente en cuanto a tiempo y valores de pH. El análisis estadístico mostró el efecto significativo de los factores material, tiempo y su interacción (p<0,01). Los resultados del análisis químico determinaron la presencia de arsénico y cromo en ambos materiales; CPM: As (2,1mg/kg), Cr (3,2mg/kg); ProRoot-MTA As (2,0mg/kg), Cr (3,5mg/kg).

Review of coagulation technology for removal of arsenic: case of Chile.

Coagulation technology has been used since 1970 in northern Chile for removing arsenic from drinking-water. This experience suggests that coagulation is an effective technology for the removal of arsenic. It is currently possible to reduce arsenic from 400 microg/L to 10 microg/L at a rate of 500 L/sec, assuming pH, oxidizing and coagulation agents are strictly controlled. The Chilean experience with the removal of arsenic demonstrates that the water matrix dictates the selection of the arsenic-removal process. This paper presents a summary of the process, concepts, and operational considerations for the use of coagulation technology for removal of arsenic in Chile.

Studies on the sorption of As(III) on the synthetic gel sodium potassium fluorophlogopite.

Sorption of As(III) has been studied on the synthesized gel close to Sodium potassium fluorophlogopite [Na0.5K0.5Mg3 (Si3 AlO10) F2] as a function of initial solution concentration at pH 2,4 and 7. The effect of parameters like equilibration time (0.5 - 24.0 hr), weight of the exchanger (30-150 mg) and temperature (25 degrees - 45 degrees c) has been investigated. The uptake of metal ion, As(III) has been expressed in terms of distribution coefficient i.e. (kd) values.

Biological process of arsenic removal using selected microalgae.

In the present investigation, growth of the organisms was reduced due to presence of arsenic (III) and (V) in the culture medium. In comparison to arsenic (V), arsenic (III) had more toxic effect on microalgae. Among the different algal strains, blue green algal species Oscillatoria-Lyngbya mixed culture showed maximum efficiency in removing arsenic (64%) after 21 days of incubation and the same algal species could remove arsenic (III), but 60% after 21 days when incubated in 0.1 mg/l arsenic (III) containing medium. Maximum removal was observed at their exponential growth phase and also so sometime extended to the stationary phase.

Batch kinetic modeling of arsenic removal from water by mixed oxide coated sand (mocs).

A new granular media developed by coating of iron and manganese on quartz sand surface proved to be effective for arsenic (III) removal from water. The media has shown alkali resistance. The kinetic and thermodynamic studies data were tested using pseudo-second- order, intraparticle diffusion and Elovich equation models. The rate constants, equilibrium sorption capacity and normalized standard deviations were calculated for all the three models. It was shown that all three models almost accurately predict the sorption capacity with respect to time for whole range of data points. However, sorption kinetic data were better correlated using Elovich equation model based on normalized standard deviation. The Langmuir and Freundlich isotherm equations could be used to describe the partitioning behavior of system at different pH and media size. The results of thermodynamic studies show that the As(III) adsorption on Mixed Oxide Coated Sand (MOCS) was endothermic in nature. Kinetic and isothermal studies data have also been used to obtain thermodynamic parameters of the process.