Brine Leaching Research Articles

Numerical modelling of the ore forming fluid migration in the sediment-hosted stratiform copper deposit, Zambian Copperbelt

As an aid to better understanding fluid flow processes and potential source rocks for the Zambian Copper Belt, preliminary numerical fluid flow modelling has been undertaken, coupled to salinity and heat transfer. The computer code used for the modelling is from Yang and Large (2001), and has been previously used to successfully model fluid flow-salinity-heat transfer in the McArthur Basin related to Stratiform Zn-Pb-Ag ore genesis (Large, et al., 2002). A 43.5km ´ 17km theoretical geological section was constructed, based on our current understanding of the structure, stratigraphy and basin architecture in the ZCB. The geological model section incorporates elements of basement, footwall succession, Ore Shale, hangingwall lower Roan siltstones and carbonates, upper Roan siltstones, carbonates and a layer of salt, Mwashia and overlying Kundelungu shales. Porosity and permeability parameters have been assigned based on our understanding of the sedimentary facies, alteration zones, petrographic evidence and local to regional structures. The most permeable elements assigned in the model are; the Mindola Clastics in the immediate footwall to the Ore Shale; crosscutting breccias in the hangingwall (below salt layer) and fault zones. The least permeable elements assigned are the Ore Shale, hangingwall carbonates and siltstones, the Mwashia shales and the basement. A one km thick salt layer in the Upper Roan has been assigned a salinity of 30 wt% (the maximum allowable by the computer code). Other sedimentary units have been given lesser initial salinities depending on the interpreted sedimentary environment (evaporitic, marine or lacustrine). A normal geothermal gradient through the basin of 30°C per km has been assumed. The model has been designed to test fluid flow and temperature gradients associated with the downward flow and convective circulation of saline fluid, from the hanging wall evaporitic salt layer into the Lower Roan stratigraphy and basement. A number of scenarios have been tested by varying the permeability of certain basin elements and fault structures. The results indicate that the most likely scenario to account for the stratiform Cu deposits involves penetration of high salinity brines from the Upper Roan salt layer down into the basement along a series on normal master faults, with brine circulation and leaching of Cu from the basement terrain. The oxidised metalliferous fluids more upwards along second order faults and are channelled into the Mindola Clastics below the organic-bearing shale cap rocks where potassic alteration and Cu-mineralisation occurs.

Zinc and lead extraction from complex raw sulfides by sequential bioleaching and acidic brine leach

This research was designed to investigate zinc and lead extraction by combined sequential biooxidation and acidic brine leaching from a raw complex sulfide ores containing sphalerite, pyrite, and galena. For the biooxidation, the zinc dissolution from the sulfide ores by the adapted bacteria was examined. The effects on ore particle size, pH, pulp density, and temperature on bacterial leaching was studied systematically. From the experiments it was shown that about 95% of zinc was extracted after 20 days of bioleaching at 30 °C. Subsequently, 98% of the lead was extracted from the bioleached residues using an acidic sodium chloride solution as the lead lixiviant at a temperature of 60 °C for 90 min leach. Leaching kinetics indicated that diffusion through the product layer was the rate controlling process during zinc bioleaching, and that the overall rate of chemical reaction at the surface was the rate controlling process during lead brine leaching. The relative activation energies of the overall rate during the two different leaching stages were calculated to be 32.09 and 44.35 kJ/mol, respectively.

Innovative processing technique to produce zinc concentrate from zinc leach residue with simultaneous recovery of lead and silver

During the conventional zinc hydrometallurgical roast-leach-electrowin process lead and silver report in the neutral leach residue along with zinc ferrite. Lead and silver from the zinc plant leach residue are recovered by a froth flotation process followed by roast-leach-precipitation-reduction to obtain a highly pure silver. Inherent process constraints of water balance and build-up of problem impurities from the silver recovery plant to the main zinc circuit, low recovery of metal values (especially lead and silver), loss of sulphur values and high cost of flotation reagents make the Mitsubishi Materials Corporation's (MMC) silver recovery process through roast-leach-precipitation-reduction technique uneconomical. Attempts have been made to make the process more effective and attractive by removing the above process constraints. An alternative and innovative approach has been developed to achieve high recovery of lead and silver, effective utilization of sulphur values and better control of impurities. The process involves the treatment of silver concentrate generated in the flotation circuit at moderate temperature-sulfuric acid leach to partially solubilise the zinc and iron and enrich lead and silver in the leach residue. The residue is treated with brine solution to solubilise most of the lead and silver which are cemented out from the leach solution with the help of aluminium to obtain a high purity lead–silver sponge which will be fed to the silver circuit to recover the metal values through a pyro-refining route. The brine leach residue which is equivalent to high quality zinc concentrate containing high levels of zinc and sulphur and minimum levels of impurities finds application as a feed to the fluo-solid roaster. This approach is different from conventional practice. The paper describes the results of moderate temperature-sulfuric acid leaching, brine leaching, quality of zinc concentrate and lead–silver sponge obtained by this proposed route with other advantages. Based on the experimental results a conceptual flow sheet has been developed. The process is simple, eco-friendly and economically viable with excellent recoveries of lead, silver, zinc and sulphur values and can be easily implemented in the existing zinc hydrometallurgical plant.

Mafic and ultramafic plutons associated with the New Madrid rift complex; a possible major source of the copper-cobalt-nickel mineralization of Southeast Missouri

The main rift structure of the New Madrid rift complex, the Reelfoot rift, strikes northeast-ward, extending from northeastern Arkansas through the Missouri and western Kentucky into southern Illinois. The recently discovered Bloomfield lineament zone transects the Reelfoot rift in the boot heel area and strikes north-northwest, passing through the Mine La Motte-Fredericktown subdistrict of the Southeast Missouri lead-zinc-copper mining district.Studies suggest a strong relationship between the proximity of the New Madrid rift complex to the Southeast Missouri district and the anomalously high amounts of Cu, Co, and Ni in the region--particularly in the Mine La Motte-Fredericktown subdistrict. Supporting evidence comes from three sources: (1) mineral zoning and paragenetic sequence, (2) geotectonics of the New Madrid rift complex, and (3) regional variations of 87 Sr/ 86 Sr and 18 O/ 16 O isotope ratios.A detailed microscopic and SEM-EDS study of the Pb-Zn-Cu ores from the Viburnum No. 28, Brushy Creek, and Goose Creek mines in the Southeast Missouri district indicates a complicated paragenetic sequence characterized by repeated periods of mineral deposition. The sequence is composed of 19 minerals including abundant galena, sphalerite, chalcopyritc, pyrite, marcasite, dolomite, calcite, and quartz as well as minor siegenite, bornite, bravoite, blaubleibender covellite, covellite, gersdorffite, digenite, enargite, tennantite, dickite, and malachite. In addition to the mineralogy and paragenetic sequence, a number of significant findings resulted from a comprehensive microscopic study of ore textures from the three mines.The paragenetic sequence of the main colloform stage of deposition indicates that the ore solutions evolved in the following general order: (1) Cu rich, (2) Co-Ni rich, (3) Pb-Zn rich, and (4) Fe rich. The general depositional sequence corresponds with mineral zoning and is similar throughout the entire lead district. Most importantly, the paragenetically early Cu-Co-Ni sulfides may represent a regional early development of the Cu-Co-Ni-rich mineralization similar to that in the Mine La Motte-Fredericktown subdistrict and the southern extension of the Viburnum Trend. This early Cu-Co-Ni-rich zone always lies at the lowest stratigraphic level and, in the Mine La Motte-Fredericktown subdistrict, indicates a southerly source for the ore fluids.It is proposed that the source of at least part of the Cu, Co, Ni, and some siderophile elements of the Southeast Missouri lead deposits may be the result of basinal brine leaching of a series of probably multiaged, mafic and ultramafic intrusions or their sediments controlled by the New Madrid rift complex. One such branch of the complex, observed on Landsat-2 imagery, is expressed as a fracture zone that extends north-northwest from the Reelfoot rift toward Fredericktown, Missouri, namely the Bloomfield lineament zone. Strong 87 Sr/ 86 Sr and 18 O/ 16 O isotope anomalies show, respectively, a consistent decrease and a consistent increase from south to north in southeast Missouri with the contour lines strikingly tracking the Bloomfield fracture zone. This suggests that the lineament zone was a channel for ore fluids entering southeast Missouri via the Mississippi embayment. The fracture zone may represent a series of transform faults or a portion of a failed continental rifting event. The zone is an epicenter trend and a distinct first-order lineament which appears to form part of the northeast boundary of the northwest-trending Missouri gravity low.

Effect of ultrasound on acidified brine leaching of double-kiln treated EAF dust

The U.S. steel industry produces approximately 500,000 tons/year of electric arc furnace (EAF) dust, which is classified as a hazardous waste. Increasing disposal costs of these dusts have encouraged studies to investigate treatment processes to render the material non-hazardous, and to possibly recover metal values. This research project was designed to examine the hydrometallurgical recovery of zinc from EAF dusts that have been treated by a double-kiln fuming process. The test work consisted essentially of acidified brine leaching of the pelletized calcine to determine the influence of traditional conditions, such as acid concentration, temperature and agitation, plus the application of ultrasound, on the zinc dissolution efficiency and selectivity. Preliminary leaching tests using acidified calcium chloride indicated that selective leaching of zinc over iron could be attained if ultrasound was employed. The effect of air and nitrogen on the leaching process was investigated and it was established that selective leaching with ultrasound was not dependent upon external agitation or on the availability of oxygen. Without ultrasound, zinc dissolution was enhanced by the presence of oxygen, while iron dissolution was greatly retarded by the absence of oxygen. The role of surface area was examined by pellet grinding and it was demonstrated that selectivity was strongly time dependent and that zinc recovery and iron rejection were enhanced at finer particle sizes. The results of the test work permitted possible mechanisms to be established for the acidified brine leaching process, and it is apparent from the results that ultrasound leaching can significantly improve the selective leaching of zinc from double-kiln treated EAF calcine.

Recovery of lead from complex sulphide leach residue by cementation with iron

Studies were made to recover lead from the leach residue obtained from ammoniacal pressure leaching of complex copper-lead-zinc sulphide bulk concentrate. The lead present as a mixture of sulphate, oxysulphate and jarosite was brought into solution by a previously standardised method consisting of sulphuric acid leaching followed by brine leaching. Lead metal from the resulting lead chloride solution was obtained by cementation with metallic iron employing conditions established in experiments conducted with chemical grade lead chloride. The rate of cementation of lead by metallic iron was found to follow a two-step process with activation energies of 40 and 60 kJ mol −1. Recovery and purity of the final lead product was very good. Based on these studies a flow sheet for recovery of lead from such material is proposed.

The effect of chloride ion on the ferric chloride leaching of galena concentrate

Previous investigations of the ferric chloride brine leaching of galena concentrate have shown that additions of chloride ion result in accelerated dissolution rates. The current study has provided the necessary information to extend and modify these previous results by incorporating the important effect of chloride ion on the dissolution kinetics. As part of this study the solubility of lead chloride in ferric chloride-brine solutions has been determined and results indicate that additions of either FeCl3 or NaCl increase the PbCl2 solubility. This is attributed to the effect of complexing on the level of free chloride ion. In addition, the dissolution kinetics of elemental lead and lead chloride were also determined and compared with the kinetics of PbS dissolution. It is significant that the rate of dissolution of PbCl2 decreases as the concentration of Cl− is decreased and as the concentration of dissolved lead increases. These results along with SEM examination of partially reacted Pb shot show that solid PbCl2 forms on the surface long before the bulk solution is saturated with lead. The PbCl2 is proposed to form by a direct electrochemical reaction between Cl− and PbS prior to the formation of dissolved lead. The reaction was determined to be first order with respect to Cl− and closely obeys the following kinetic model based on a rate limiting charge transfer reaction at the surface: $$1 - (1 - a)^{1/3} \left[ {\frac{{5.01x10^{11} }}{{r_0 }}\left[ {Fe^{3 + } } \right]_T^{0.21} \left[ {Cl^ - } \right]_T^{1.0} \exp \left( {\frac{{ - 72100}}{{RT}}} \right)} \right]t$$ The model is in excellent agreement with experimental results up to about 95 pct reaction as long as the solubility of PbCl2 is greater than about 0.051 M. Where these conditions are not met, deviation from the surface reaction model occurs due to the extremely slow dissolution rate of PbCl2. Therefore the effect of Cl− on the brine leaching of PbS is attributed to two factors, the direct reaction of Cl− with the pbS surface and the effect of Cl− on the dissolution rate of PbCl2. The overall dissolution process is viewed as occurring in three stages; in the first stage the reaction is controlled by the surface reaction and described by the model above, then as solid PbCl2 is produced the diffusion of Cl− would be equal in importance with the surface reaction,i.e, the second stage. As the reaction proceeds further, a shift in the rate-limiting step from surface reaction to product layer or pore diffusion occurs, the third stage. Thus the rate-determining step would no longer be just the surface reaction as observed experimentally at longer reaction times. The practical implications of these results for the processing of a complex sulfide concentrate using sequential, selective, or total leach approaches are also discussed.

An investigation of the thermodynamics and kinetics of the ferric chloride brine leaching of galena concentrate

The solution thermodynamics of acidified ferric chloride brine lixiviants and the dissolution kinetics of a galena concentrate in such solutions have been investigated. The distribution of the various metal chloro complexes calculated from available thermodynamic data shows that the distribution is shifted to the higher complexes, predominantly FeCl3o, FeCl2o, and PbCl4=, as the total Cl− concentration increases, and that the distribution is unaffected by the extent of reaction. The dissolution of PbS concentrate is presented as a competition between a nonoxidative reaction with H+ and the oxidative reaction with ferric ion. Acid dissolution of PbS predominates when the activity ratio of hydrogen ion to ferric ion is high. Under these conditions H2S is produced. When the activity ratio of hydrogen ion to ferric ion is low, and especially when the concentration of Fe3+ is greater than 0.15 M, oxidative dissolution of PbS becomes the controlling reaction. The dissolution can be represented by a shrinking core model with a surface chemical reaction as the rate controlling step. This is supported by the activation energy of 72.1 kJ/mole and the dependence of the rate on the inverse of the particle radius. The following rate equation was found to be in excellent agreement with the experimentally observed leaching behavior for 0.15 to 0.6 M [Fe+3]T up to approximately 90 to 95 pet extraction: $$1 - \left( {1 - \alpha } \right)^{1/3} = \left[ {\frac{{2.3 x 10^{12} }}{{r_0 }}\left[ {{\text{Fe}}^{{\text{ + 3}}} } \right]_T^{0.21} \exp \left( {\frac{{ - 72100}}{{{\text{R}}T}}} \right)} \right]t$$ The rate deviates from the 0.21 order for Fe+3 concentrations greater than 0.6 M. The deviation from the surface model at higher values of PbS conversion is due to the presence of solid PbCl2 in the pores of the reacting particles.

The mobilization of selected trace metals from shales by aqueous solutions; effects of temperature and ionic strength

Removal of trace metals from shales by subsurface brines is often suggested as an origin of base metals in low-temperature, strata-bound ore deposits. This investigation studied the hypothesis that brine leaching of shales can increase metal content of subsurface brines sufficiently that the brines could potentially serve as ore-forming fluids. Two aspects were studied: the effect on mobilization of changes in the brine temperature (25 degrees , 50 degrees , and 90 degrees C) and of changes in the ionic strength (0, 0.7, 2.0, and 4.0). The results of this study support the hypothesis. The following observations were made: (1) Increasing either the temperature or ionic strength of the brine increased the amount of leaching, but the trends were neither simple nor linear; a brine with an ionic strength of 10 at 120 degrees C might not be any more effective in leaching trace metals than a brine with an ionic strength of 5 at 90 degrees C. (2) Changing the salt composition of the brine changed the amount and type of mobilization. Calcium, for example, was found to be effective in leaching Pb and Zn, while K was found to be effective in mobilizing Cu.