سپیده جوانشیر

In this work, zinc extraction from an industrial leach solution was investigated by saponified di(2-ethylhexyl)phosphoric acid (D2EHPA). The solution obtained was from a bioleaching process of a low-grade lead-zinc sulfide ore that contained 50 g/L of zinc and 6.3 g/L of iron. The selective and high Zn(II) extraction yield were obtained by modification of D2EHPA in a proposed two-step process. Firstly, a significant amount of iron (87%) was removed as sodium-jarosite via precipitation from the pregnant leaching solution (PLS) prior to zinc extraction, and secondly, the effective parameters involved in zinc extraction including the contact time, saponification degree, type of saponifier, stirring speed, pH, temperature, D2EHPA concentration, and phase ratio (A:O) were investigated. The results obtained showed that 98.4% of zinc could be extracted under the optimum conditions, i.e. 20% D2EHPA, 15% saponification degree, 650 rpm, pH 2, and an A:O ratio of 1:1 at the ambient temperature (25 ± 2 °C) during 90 s; it was 25% higher than using non-saponified D2EHPA under the same conditions. Moreover, while one theoretical step was required for the complete extraction of zinc by saponified D2EHPA, the required number of steps using D2EHPA was about three. Therefore, the advantages of the process would be two-fold: reducing the number of extraction stages and no need for neutralizing the raffinate in every extraction stage.

The wastewaters of the mining and metallurgical activities must be treated before discharging into the environment due to the highly toxicity of cyanide. One of the most efficient technologies for the removal of cyanide from wastewaters is adsorption. In this research, layered double hydroxides (LDHs) known as anionic clays was synthesized by co-precipitation process using a 3:1 ratio of magnesium nitrate and aluminum nitrate and used for removal of cyanide from aqueous solutions. The chemical and mineralogical compositions of LDH were investigated using XRD, XRF and Scanning Electron Microscopy (SEM) and Wavelength Dispersive X-ray (WDX) analysis methods. The largest particle size of LDH was determined about 4 nm using Scherrer equation which indicates that the synthesized LDH is in the range of nano-sized materials. The effect of temperature, absorbent dosage, stirring speed and pH on the adsorption capacity of LDH for cyanide was investigated using experimental design method by DX7 software. The optimum conditions were determined to be temperature=60oC, adsorbent weight=1.5 g, rotation speed=500 rpm and pH=9.52. In this condition, the maximum adsorption capacity of synthesized LDH for cyanide was 73.80 mg/g. The equilibrium data and the kinetic data were best modeled by Langmuir isotherm model and pseudo-second-order kinetic model, respectively. The rate limiting step was determined to be intraparticle by adopting the adsorption data with Weber and Morris model and the adsorption of cyanide onto LDH is occurred through ion-exchange mechanism due to chemical composition and mineralogical structure of LDH. LDH synthesized using salts of industrial purity also showed high potential for removal of cyanide ions from the solution. Also, the treatment of a real wastewater by LDH showed that with an absorbent dose of 20 g /L, more than 84% of the cyanide can be removed from the wastewater.

Flotation is the most commonly used process for desulfurization of iron concentrates in iron beneficiation plants. The current study deals with improving the metallurgical performance of the flotation circuit at Sangan iron beneficiation plant. A plant survey indicated that sulfur content of iron concentrate is sometimes higher than that of the permitted limit used for the pelletizing plants (<0.25%). For this purpose, laboratory and full-scale experiments were carried out. In the batch flotation tests, the effect of collector dosage (65-105 g/t), frother dosage (45-75g/t), pH (6-10) and slurry solid content (27-33%) was examined against sulfur recovery. The results showed that the collector dosage, pH, frother dosage and slurry solids% are the most significant parameters in terms of sulfur recovery, respectively. The metallurgical performance improved with increasing the collector and frother dosage as well as reducing the pH. In the plant site tests, the influence of collector distribution method in the flotation circuit, collector dosage (65-105 g/t), frother dosage (37-85 g/t) and slurry solids% (25-33 g/t) on the flotation circuit performance was investigated. The results indicated that the optimum metallurgical performance was achieved when collector addition is divided into three parts: 50% was added to the rougher feed, 30% to the cleaner feed and 20% to the scavenger feed. Increasing the collector and frother dosage resulted in an increase in the sulfur recovery and a reduction in iron concentrate sulfur content. Increasing the slurry solids% was found to be beneficial to the sulfur recovery and detrimental to the quality of the product.

Effective parameters on diluent quality in copper solvent extraction circuit have been investigated. Several experiments were carried out with 10% CP150 as extractant in 90% diluent with different aromatic contents (5-35%). Performance parameters such as kinetics, selectivity, separation time and entrainment have showed that, by increasing the aromatic content in diluent, the copper extraction rate, separation time and losses of extractant by entrainment have been decreased; If aromatic content increased from 5 to 35 %, entrainment and separation time declined about 50 % while aromatic content appears to help suppress iron co-extraction. Batch experiments repeated by several composition prepared from various ratios of Kerosene, Reasol 8401 and Reasol 8411. Results indicated that aromatic content of diluent must be controlled as well as physical properties especially where a mixture of several solvents are used as diluent. Low diluent viscosity improve the kinetics because of high phase dispersion; if diluent viscosity increase from 2.09 to 2.29 cSt, extraction rate in 30 seconds is reduced by 30%. Higher density and surface tension result in organic phase entrainment and solvent loss; so that, by increasing in surface tension from 26 to 27/3 mN/m, entrainment enhanced by almost 100%. However, high interfacial tension, density and viscosity enhanced Cu/Fe separation; if diluent density rise up 35 Kg/m3, Cu/Fe transmission factor is declined tenfold.

In this research، a video technique was developed by a digital camera (Canon، 12 MPixel)، to measure the organic drop size in the mixer-settler. For drop size determination، the recorded pictures (in the output of the mixing chamber) were analysed with Clemex software. Then the Sauter mean diameter was calculated. The effects of different parameters such as stirring speed، aqueous and organic volumetric flow rate، holdup، gold and DBC concentration on gold extraction have been reported. The Increase of stirring speed (in rang of 335 - 600 rpm) had a direct effect on drop breakage and number of smaller drops، consequently higher gold extraction by about 50 % was obtained. As it is shown in figure 3، D32 depends on the impeller speed (N) as a power function with the average exponent of -1. 43. Hence، the results verified the Hinze- Kolmogorov’s theory. The enhancement of aqueous volumetric flow rate from 16 ml/min to 50 ml/min causes short contact time in the system and resulted in decreasing the extraction about 35 %. However، when organic flow rate (Holdup) rose more than 30ml/min، phase inversion occurred and gold extraction decreased. By comparing the results، it was found that it is better to fix aqueous phase volume flow rate and change organic one to get good result in the industrial scale. The gold concentration in aqueous phase had an important effect on the physical property of system like interfacial tension. Lower interfacial area in the higher gold concentration resulted in smaller drops. Therefore، E% increased about 50 % at the same conditions. For the DBC concentration range between 60 and 100 %، drop size decreased most sharply with increasing the concentration، because the interfacial tension was diminished considerably. Furthermore، this decrease was due to the drops breakage and consequently، higher gold extraction about 4. 5 timeswas obtained.