A new oxalic acid (H2C2O4) and hydrogen peroxide (H2O2) based extraction process was developed to recover valuable metals in particular Ga and Ge from the zinc refinery residues. H2C2O4 and H2O2 leaching studies indicated that the selective leaching of metals in the residues, that primarily contain Zn, Cu, Fe, SiO2, Ga and Ge, can be achieved. Under the optimal leaching conditions ([H2C2O4] = 110 g/L, [H2O2] = 0.12 mol/L, L/S ratio = 8, T = 40 °C and t = 30 min), 99.32% of the Ga, 98.86% of the Ge and 30.25% of the Fe were leached out, whereas the leaching of Zn, Cu and Si only reached 0.30%, 0.82% and 0.43%, respectively. Concerning leachate purification, 98.31% of the iron could be removed in the form of FeC2O4·2H2O with minor losses of Ga and Ge (1.08% and 0.68%) using an ultrasound-assisted iron powder replacement method under optimal conditions. The Ga (99.36%) and Ge (99.89%) were subsequently extracted by tri(octyl-decyl)amine (N235). After extraction, the loaded organic phase was stripped of Ga (98.91%) and Ge (99.21%) into separate solutions using sequential treatments of 2 mol/L H2SO4 and 4 mol/L NaOH respectively. Based on these results, a process flow sheet of efficient separation and recovery of Ga and Ge is presented.
Enrichment and migration regularity of coal particles in compound force field provided by Falcon concentrator were studied. Influence of centrifugal force and fluidization water pressure on the distribution rates and ash contents of materials that enriched in overflow, top separation area and bottom separation area were tested respectively. Radial velocity of fluidization water, having an important influence on the sedimentation of particles, was calculated and results show that radial velocity of fluidization water in top groove is greater than that in bottom groove, which contributed to the selectivity and recovery of combustible. Besides, density composition of products in different enrichment areas was studied. Results show that in the upward migration process, particles with high density are gradually captured. Therefore, the material density is gradually reduced from bottom to top separation area. Meanwhile, mismatch phenomena occurred as the existence of heavy particles in overflow, and light particles in the grooves. Based on the morphology analysis, it is can be deduced that particles mismatch is the results of the increase of drag coefficient since the irregular shape.
To understand the effect of aqueous impurities on chalcopyrite dissolution during acid metalliferous drainage and hydrometallurgical processes, batch dissolution experiments were carried out at 650 and 750 mV (SHE), pH 1 and 35-75 degrees C in the presence or absence of aqueous cationic additives. Activation energies (E-a) for chalcopyrite dissolution in the presence of additives at 750 mV, derived using a modified 'time to a given fraction' method, demonstrate that E-a varies with reaction extent. The overall trend of evolution from interface- to transport controlled mechanism was independent of additive type or addition. This suggests that it is not primarily variation in the enthalpy of dissolution that controls the significant changes in relative dissolution rates on addition of additives. Rather, the relative dissolution rates on addition of aqueous cations are found to relate to the M-O framework volume (M and O being the cationic additive and oxygen within H2O in the first sphere of hydration, respectively). There is good inverse linear correlation between this volume and the relative dissolution rate per unit ionic strength which varies as K+ > Al3+ > no additive > Mg2+ > Na+ > Ca2+. It is proposed that this effect is related to the relative strength of hydration of the additives with the commensurate entropic effect on solute hydration being advantageous for chalcopyrite dissolution on K+ and Al3+ addition and detrimental for the other additives. R4SiO4, the dominant aqueous species upon Si addition under the conditions examined, has low affinity for water, resulting in a detrimental entropic contribution to solute hydration and dissolution. The effect of Fe addition on relative dissolution rate is convoluted by the role of Fe3+ as the primary oxidant for chalcopyrite dissolution. On addition of aqueous Fe to dissolution at 750 mV, the effect is detrimental due to the detrimental effect on the entropy of hydration of the solute and the relative abundance of Fe3+. At 650 mV the effect of the greater presence of Fe3+ due to Fe addition dominates and the dissolution rate is enhanced. (C) 2016 Elsevier B.V. All rights reserved.
An experimental study is conducted to investigate the effect of filling interval time (FIT) on the uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) of cemented coarse tailing backfill (CCTB). A total of 72 CCTB samples with diameter×height of 50mm×100mm prepared at different solid contents (70, 72, and 75wt%) and water-to-cement ratios (3.00, 2.72, and 2.33) were subjected to UPV and UCS tests at 12, 24, 36 and 48h of FIT. The UCS and UPV values of the CCTB samples increased with the increase in the solid content. However, an increase in FIT led to a decrease in the UPV and UCS of the CCTB samples. Different types of curve fittings were conducted to obtain the correlation between UPV and UCS versus FIT at different solid contents. A polynomial function can explain the relationship between UPV and FIT. Moreover, the UCS and UPV values exhibit a linear function. CCTB also shows a failure mode of tensile failure-tensile shear failure transition-tensile and shear mixing failure modes, which provides a theoretical basis for the strength design and stability control of backfills.
