Removal and stabilization of arsenic from anode slime by forming crystal scorodite

A process was proposed for removing and stabilizing arsenic(As) from anode slime. The anode slime with high arsenic concentration was pretreated by circular alkaline leaching process. Then, the arsenic in the leaching solution can be further precipitated as a form of scorodite crystalline(FeAsO4·2H2O). In the precipitating arsenic reaction, in which ferrous ions were oxidized by air gas, the effects of acidity(p H), reaction temperature, air flow rate, initial concentration of arsenic and initial molar ratio of Fe(II) to As(V) on arsenic precipitation were investigated. The results showed that sufficiently stable crystal scorodite could be achieved under the condition of initial arsenic concentration of 10 g/L, pH 3.0-4.0, Fe/As molar ratio of 1.5, the temperature of 80-95 °C, and the air flow rate higher than 120 L/h. Under the optimal condition, more than 78% of arsenic could be precipitated as a form of scorodite crystalline. The As leaching concentration of the precipitates was less than 2.0 mg/L and the precipitates may be considered to be safe for disposal.

Effect of arsenopyrite on thiosulfate leaching of gold

Arsenopyrite was artificially added into the thiosulfate leaching solution to clarify the role of arsenopyrite on the thiosulfate leaching of gold.The effect of arsenopyrite on the thiosulfate leaching of gold was studied by the thermodynamic calculation,mineral dissolution test,leaching test and XPS analysis.The results show that the thiosulfate consumption slightly increases with increasing the concentration of arsenopyrite,but the gold dissolution is obviously hindered.This may mainly attribute to the catalytic effect of arsenopyrite on the thiosulfate decomposition and the formation of passivation layer on the gold foil surface.The passivation layer likely consists of Cu2S or Cu（S2O3）35-,element S,FeOOH and iron arsenate,which is deduced from the XPS analysis.However,the negative effect of arsenopyrite can be eliminated by adding additives.It is found that both additives of sodium carboxymethyl（CMC） and sodium phosphate（SHPP） can not only decrease the thiosulfate consumption but also improve the gold dissolution.

Stabilization of ferric arsenate sludge with mechanochemically prepared FeS2/Fe composites

FeS2/Fe composites were mechanochemically prepared with iron powder and pyrite for the stabilization of ferrite arsenate sludge(FAS).The effects of preparation parameters on stabilization performance were investigated.The results show that the optimum conditions are FeS2/Fe molar ratio of 5:5,milling time of 2 h,ball-to-material mass ratio of 15:1 and milling with stainless steel ball.Then,the composites were characterized by XRD,SEM,FTIR,etc.The physicochemical properties of FeS2/Fe mixture change dramatically,which is responsible for its excellent performance.Finally,the stabilization process of FAS was optimized.When the FAS is mixed with composites at mass ratio of 4:1 and milled for 30 min,the As leaching concentration of FAS can be reduced from 639.15 to 4.74 mg/L with the stabilization ratio of 99.2%.

Formation of arsenic−copper-containing particles and their sulfation decomposition mechanism in copper smelting flue gas

The heat recovery steam generator(HRSG)of copper smelting generates a large number of arsenic−coppercontaining particles,and the in-situ separation of arsenic and copper is of importance for cutting off environmental risk and realizing resource recovery.The formation of arsenic−copper-containing particles was simulated,the method of in-situ decomposition of arsenic−copper-containing particles by pyrite was proposed,and the decomposition mechanism was confirmed.It was found that particles with high arsenic content were formed in the simulated HRSG,and copper arsenate was liable for the high arsenic content.Pyrite promoted the sulfation of copper,leading to the in-situ decomposition of copper arsenate.In this process,gaseous arsenic was released,and thus the separation of arsenic and copper was realized.

Microstructure and magnetic properties of FeAs with coarse-grain and nanocrystalline structure

The microstructure and magnetic properties of iron arsenide(FeAs) with coarse-grain and nanocrystalline structure were investigated. Coarse-grain FeAs was synthesized through high-energy ball milling and heat treatment. Nanocrystalline FeAs was obtained by ball milling of coarse-grain FeAs. The results suggest that the reduced grain size of FeAs(from >100 to 32.4 nm) is accompanied by the introduction of internal strains up to 0.568% with ball milling time from 0 to 32 h. The magnetic properties of FeAs show that the coercivity is reduced from 29.2 to 15.6 kA/m and the magnetization is increased over time of milling. The low coercivity is mainly due to the small grain size stemmed from ball milling, while the increase of magnetization is primarily caused by the change of lattice parameters of FeAs and the emergence of superparamagnetic phase at the same time.

Physicochemical properties of arsenic-bearing lime-ferrate sludge and its leaching behaviors

Physicochemical properties and leaching behaviors of two typical arsenic-bearing lime?ferrate sludges(ABLFS),waste acid residue(WAR)and calcium arsenate residue(CAR),are comprehensively described.The chemical composition,morphological features,phase composition and arsenic occurrence state of WAR and CAR are analyzed by ICP?AES,SEM?EDS,XRD,XPS and chemical phase analysis.The toxicity leaching test and three-stage BCR sequential extraction procedure are utilized to investigate arsenic leaching behaviors.The results show that the contents of arsenic in WAR and CAR are2.5%and21.2%and mainly present in the phases of arsenate and arsenic oxides dispersed uniformly or agglomerated in amorphous particles.The leaching concentrations of arsenic excess119and1063times of TCLP standard regulatory level with leaching rates of47.66%and50.15%for WAR and CAR,respectively.About90%of extracted arsenic is in the form of acid soluble and reducible,which is the reason of high arsenic leaching toxicity and environmental activity of ABLFS.This research provides comprehensive information on harmless disposal of ABLFS from industrial wastewater treatment of lime?ferrate process.

Redox behavior and chemical species of arsenic in acidic aqueous system

Arsenic(As)removal from smelting acidic wastewater is an urgent task.The most common method is oxidation of trivalent As(III)to pentavalent As(V)subsequently precipitated by ferric(Fe(III))salts.Foundations of redox behavior and chemical species are of great importance for understanding As removal.In this work,cyclic voltammetry(CV)and UV?Vis spectroscopy were used for laboratory observation;meanwhile HSC and MINTEQ software were employed for theoretical analyses.It is found that As(III)oxidation,a multiple electron transfer reaction,is diffusion-controlled.The oxidation over-potential is very high(about0.9V)in sulfuric acid solutions(pH1.0).In addition,Fe(III)?As(V)complexes are evidenced by UV?Vis spectra and chemical species analyses in series of Fe(III)?As(V)?H2SO4?H2O solutions.Therefore,the Fe(III)and As(V)species distribution against pH values are determined and a newφ?pH diagram with inclusion of Fe?As complexes is consequently compiled based on thermodynamic data predicted by other researchers.

Iron Activation of Natural Aluminosilicates to Remove Arsenic from Groundwater

Low-cost adsorbents constituted by Fe-modified-aluminosilicates （laminar and zeolite type minerals） were developed and characterized to be used in the arsenic removal from groundwater. Iron activation was carried out ＂in situ＂ by the synthesis and deposition of mesoporous ferrihydrite. Natural iron-rich aluminosilicate was used as reference. All samples were characterized by X-ray diffraction, Raman spectroscopy, BET N2-adsorption, SEM-EDS microscopy and ICP chemical analysis. Experimental results of arsenic sorption showed that iron-poor raw materials were not active, unlike iron activated samples. The iron loading in all activated samples was below 5% （expressed as Fe203）, whereas the removal capacity of these samples reaches between 200-700 gg of As by g of adsorbent, after reusing between 17 cycles and 70 cycles up to adsorbent saturation. Differences can be associated to mineral structure and to the surface charge modification by iron deposition, affecting the attraction of the As-oxoanion. On the basis of low-cost raw materials, the easy chemical process for activation shows that these materials are potentially attractive for As（V） removal. Likewise, the activation of clay minerals, with natural high content of iron, seems to be a good strategy to enhance the arsenic adsorption ability and consequently the useful life of the adsorbent.

The anomalous Hall effect in epitaxial Fe(110) films grown on Ga As(110)

The anomalous films grown on GaAs（110） Hall effect in epitaxial Fe（110） is investigated as a function of both film thickness and temperature. The Berry curvatureinduced intrinsic contribution of 996 Ω^-1 cm^-1 is determined experimentally for the first time. Together with 821 Ω^-1 cm^-1 in Fe（111） and 1100 Ω^-1 cm^-1 in Fe（001） obtained earlier, we show unambiguously the anisotropy of the Berry curvature contribution to the anomalous Hall effect in single-crystal Fe.

Surface chemistry of polymer-supported nano-hydrated ferric oxide for arsenic removal: effect of host pore structure

Immobilization of hydrous ferric oxide(HFO) particles inside solid hosts of porous structure is an important approach to improve their applicability in advanced water treatment such as arsenic and heavy metal removal. Here, we fabricated three polystyrene(PS)-based nano-HFOs and explored the effect of host pore structure on the surface chemistry of the immobilized HFOs. Potentiometric titration of the hybrids and surface complexation modeling of their adsorption towards arsenite and arsenate were performed to evaluate the surface chemistry variation of the loaded HFOs. Polymer hosts of higher surface area and narrower pore size would result in smaller particle size of HFOs and lower the value of the point of zero charge. Also, the site density(normalized by Fe mass) and the deprotonation constants of the loaded HFOs increased with the decreasing host pore size. Arsenite adsorption did not change the surface charge of the loaded HFOs, whereas arsenate adsorption accompanied more of the negative surface charges. Adsorption affinity of both arsenic species with three HFO hybrids were compared in terms of the intrinsic surface complexation constants optimized based on the adsorption edges. HFO loaded in polystyrene host of smaller pore size exhibits stronger affinity with arsenic species.