Application of Response Surface Method and Central Composite Design for Modeling and Optimization of Gold and Silver Recovery in Cyanidation Process

In this study, application of the Response Surface Methodology and the Central Composite Design (CCD) technique for modeling and optimization of the influence of several operating variables on titanium recovery in a leaching process were investigated. The four main leaching parameters, namely temperature, acid concentration, leaching time and solid to liquid ratio, were changed during-the leaching experiments based on the CCD. A total of 30 leaching experiments were designed and carried out in the CCD method according to software-based designed matrix. According to the results, i.e., titanium recoveries with these four parameters as well as empirical model equations were developed. The model equations were then individually optimized by using quadratic programming to maximize titanium recoveries for both ilmenite and slag within the experimental range. The predicted values for titanium recoveries for both ilmenite and slag were found to be in a reasonable agreement with the experimental values, with R2 as correlation factor being 0.963 and 0.916 for ilmenite and slag, respectively.

The aim was to assess the technological feasibility of generating sodium cyanide by coal gasification, to study the effects of the process parameters (temperature, experiment duration, coal type) on the concentration of sodium cyanide in the resulting solutions, as well as to identify optimal modes of the process. Experiments were carried out on a laboratory setup consisting of a tubular cylindrical furnace equipped with a working compartment in the form of a corundum tube. Lignite and charcoal, preliminarily crushed to increase the specific surface area, were investigated. A solution of sodium cyanide was produced by sorption of gaseous hydrocyanic acid (a syngas component) with a sodium carbonate solution. A NaOH solution (pH = 10) installed in an ice bath was used in the system of absorbers. The content of sodium cyanide in the solution was determined by the titrimetric method. The HSC Chemistry 5.1 software package was used for thermodynamic calculations. During the gasification of charcoal in the temperature range 600–800oC, sodium cyanide solutions with a concentration of 0.03–0.08 wt% were obtained. An increase in temperature from 600 to 900oC led to a 4-fold decrease in the concentration of sodium cyanide in an alkaline solution, under the same duration of the experiments. A regression equation was derived for the dependence of the NaCN concentration in solution on the temperature of coal gasification and the duration of the process. It was shown that the generation of sodium cyanide by coal gasification under laboratory conditions yields sodium cyanide concentrations in solution comparable to those used for gold cyanidation at gold recovery plants. The installation of sodium cyanide generation lines directly at the production areas of gold recovery plants will reduce the production costs by eliminating expenses for purchasing, transporting and storing reagents.

Bio-dissolution of Cu, Mo and Re from molybdenite concentrate using mix mesophilic microorganism in shake flask

The aim of this study was to evaluate the technological feasibility of producing sodium cyanide through coal gasification. Specifically, it examined the effects of key process parameters—temperature, experiment duration, and coal type—on the concentration of sodium cyanide in the resulting solutions, and aimed to identify the optimal operating conditions. Experiments were conducted using a laboratory-scale setup consisting of a tubular cylindrical furnace with a corundum tube as the working compartment. Lignite and charcoal, pre-crushed to increase their specific surface area, were used as feedstocks. Sodium cyanide was produced by sorbing gaseous hydrogen cyanide (a component of the syngas) into a sodium carbonate solution. An NaOH solution (pH = 10), maintained in an ice bath, was used in the absorber system to stabilize the cyanide. The concentration of sodium cyanide in the final solution was determined using a titrimetric method. The thermodynamic modeling was performed using the HSC Chemistry 5.1 software package. When charcoal was gasified at temperatures between 600 °C and 800 °C, sodium cyanide concentrations in the range of 0.03–0.08 wt.% were obtained. However, increasing the temperature from 600 °C to 900 °C resulted in a fourfold decrease in sodium cyanide concentration under otherwise constant conditions. A regression equation was derived to express the dependence of sodium cyanide concentration on gasification temperature and reaction duration. The findings demonstrate that sodium cyanide generation via coal gasification under laboratory conditions can yield solution concentrations comparable to those employed in gold cyanidation at industrial gold recovery plants. Establishing on-site sodium cyanide generation at gold processing facilities could significantly reduce production costs by eliminating the need for purchasing, transporting, and storing commercial cyanide reagents.

In view of the difficulty in recovering valuable metals and cyanides from cyanide tailings pulp in gold mines, the laboratory exploratory test of recovering gold and silver from the tailings pulp produced by a CIP process was carried out by using the technology of “solid-liquid separation + membrane separation and purification + adsorption and recovery of gold and silver by activated carbon”. The results showed that the cyanide tailings slurry was separated by solid-liquid in the laboratory and stabilized by chemicals, and the dry slag was identified as a general solid waste according to the results of the identification standard for hazardous waste leaching toxicity GB5085.3-2007. The screened reverse osmosis membrane test showed that 95% of the permeate water recovery rate were obtained. The concentration of cyanide in membrane concentrate water reached 807.9 mg/L, the concentration of copper, gold and silver reached 0.43 mg/L and 3.91 mg/L respectively after being concentrated from below the detection limit, and the concentration was 19.9, 14.3 and 18.6 times respectively. The adsorption test of membrane concentrate water by activated carbon showed that gold, silver and copper were absorbed in membrane concentrated water, the adsorption rates reached 99.76%, 96.16% and 9.09% respectively, which facilitated the subsequent selective recovery of gold and silver. The recovery of valuable metals and cyanide from cyanide tailings slurry by the process of “solid-liquid separation + membrane separation and purification + adsorption and recovery of gold and silver by activated carbon” had a good effect.

The aim was to assess the technological feasibility of generating sodium cyanide by coal gasification, to study the effects of the process parameters (temperature, experiment duration, coal type) on the concentration of sodium cyanide in the resulting solutions, as well as to identify optimal modes of the process. Experiments were carried out on a laboratory setup consisting of a tubular cylindrical furnace equipped with a working compartment in the form of a corundum tube. Lignite and charcoal, preliminarily crushed to increase the specific surface area, were investigated. A solution of sodium cyanide was produced by sorption of gaseous hydrocyanic acid (a syngas component) with a sodium carbonate solution. A NaOH solution (pH = 10) installed in an ice bath was used in the system of absorbers. The content of sodium cyanide in the solution was determined by the titrimetric method. The HSC Chemistry 5.1 software package was used for thermodynamic calculations. During the gasification of charcoal in the temperature range 600–800oC, sodium cyanide solutions with a concentration of 0.03–0.08 wt% were obtained. An increase in temperature from 600 to 900oC led to a 4-fold decrease in the concentration of sodium cyanide in an alkaline solution, under the same duration of the experiments. A regression equation was derived for the dependence of the NaCN concentration in solution on the temperature of coal gasification and the duration of the process. It was shown that the generation of sodium cyanide by coal gasification under laboratory conditions yields sodium cyanide concentrations in solution comparable to those used for gold cyanidation at gold recovery plants. The installation of sodium cyanide generation lines directly at the production areas of gold recovery plants will reduce the production costs by eliminating expenses for purchasing, transporting and storing reagents.

This research focuses on the hydrometallurgical processing of auriferous ores and their processing products, namely, flotation and gravity concentrates. The main valuable component of an ore sample of any deposit is gold. The gold content should be in the range of 11.11–12.87 g/ton. The main rock-forming minerals of the original ore are quartz (60.1%), quartz–chlorite–micaceous aggregates (3.8%), and carbonates (7.1%). In this study, original ores of various sizes were treated by direct and sorption cyanidation under various leaching modes, and the results obtained were presented. The original ore was leached with various concentrations of sodium cyanide (NaCN) in solution to study the effect of the complexing agent concentration on gold recovery. Data on the dynamics of leaching revealed that a decrease in the concentration of NaCN in solution from 0.2% to 0.03% leads to a decrease in gold recovery in solution by 26.81%. Original ores could easily be processed using hydrometallurgical methods. The recovery of gold with a coarseness of 95% − 0.045 mm from the original ore averaged 97.77%. This work features a full range of studies on the hydrometallurgical processing of concentrates and gravity tailings, as well as the effects of flotation concentration of gold recovery. The gravity concentrate is resistant to intensive cyanidation (i.e., only 67.07% gold recovery into the solution). The use of 1% lead nitrate (PbNO3) during intensive cyanidation could reduce the refractoriness of the concentrate and increase the recovery of gold into the solution by up to 94.35%. The total gold recovery from gravity concentrate is 98.71%, and the recovery of gold by cyanidation of gravity tailings with a cyanide concentration of 0.2% averages 96.57%. The recovery of gold during leaching of the flotation concentrate at the original size (95.5% − 0.074 mm) and a cyanide concentration of 0.2% is 96.64%. A decrease in the size of the flotation concentrate from 95.5% − 0.074 mm to 95% − 0.02 mm leads to a decrease in gold recovery by 35.43% because of the strong chemical activation of the material during grinding.

On the use of lignin-based biopolymer in improving gold and silver recoveries during cyanidation leaching

Treatment of pyritic matrix gold–silver refractory ores by ozonization–cyanidation

Gold recovery improvements in grinding and flash flotation circuit

Remediation of reduced sulfur species effects on gold and silver recovery during cyanide leaching

Ultrasound-based biodiesel synthesis using waste cotton-seed cooking oil (WCCO) is significant because it is a highly energy-efficient process and the reaction time also gets cut down. This chapter is focused on the comparison of optimization results of a biodiesel production from WCCO catalyzed by KOH via an ultrasound (US)-based transesterification process using response surface methodology-based box-Behnken design (BBD) and central composite design (CCD) methods. Quadratic polynomial equations are obtained by analyzing experimental values for transesterification reaction. To reinforce the biodiesel yield following parameters are considered: methyl alcohol: oil ratio (molar ratio), KOH amount (wt%), and process temperature. The impact of these parameters on biodiesel yield is inspected by different plots. It was observed that the catalyst amount was the foremost prominent parameter on the biodiesel for both BBD and CCD methods. The process variables optimized for biodiesel yield were in a good match for BBD and CCD methods individually – methyl alcohol: oil molar ratio: 6:1, KOH wt%: 0.50%, reaction temperature: 50 ºC, and process biodiesel yield: 98%. An imperative connection with experimental results brings an R2 value of 98.66% for BBD method, while in CCD method, R2 value is 99.95%.

Over the past decade the concern about toxic metals in freshwater has increased. Environmental laws such as the Clean Water Act have forced industries that produce metal containing wastewater to treat their wastewater prior to discharge. The purpose of this study was to investigate the use of a novel method for the minimization of heavy metals in the wastewater from the mining industry. A very promising electrochemical treatment technique that does not require chemical additions is electrocoagulation (EC) and sulphide precipitation. The present study has been done for the recovery of gold and silver contained in pregnant solution from the cyanidation process using the electrocoagulation technology with iron electrodes; that is a developed alternative technology for the Merril-Crowe process. The average gold and silver content in pregnant solution was 4.27 and 283 ppm respectively and the recoveries were 92% for gold and 95% for silver, with optimum operating parameters of pH 10, residence time of 20 minutes and addition of sodium chloride of 4 gr/L. The results of precipitation process show that the elimination of lead, zinc, cooper and iron ions from the barren solution was successful, with optimum operating parameters of pH 3 and residence time of 15 minutes, and the recoveries were 99% of these ions. Finally the characterization of the solid products of gold and silver formed during the EC process with Scanning Electronic Microscope was performed. Results suggest that magnetite particles and amorphous iron oxyhydroxides (lepidocrocite) were present.

A new method for the recovery of gold has been developed using sodium cyanide as a leaching agent. Zinc powder was used for the deposition of gold. Effect of various parameters like time of air passage, concentration of leaching agent and time of deposition of gold on zinc for maximum recovery of gold from ore have been studied. 0.1% concentration of sodium cyanide is required for the maximum recovery of gold when the period of air passage is 24 hours. The amount of gold recovered depends upon the time allowed for deposition which for 100 gms of sample was observed to be 15 hours in our experiments.

The global amount of end-of-life mobile phones is increasing over the years and their proper valorization is nowadays of strategic importance. Mobile phones can be considered as an important source of valuable materials, such as metals, plastics, and glass, which can be recovered and reintroduced into new production cycles. In this paper, a recovery process based on selective materials’ separation and hydrometallurgy was proposed. After manual dismantling followed by the separation of the different fractions (plastic, metallic fraction, printed circuit boards, batteries, displays and glass), a hydrometallurgical process based on leaching and precipitation/reduction was applied on printed circuit boards with the aim of recovering the metals of interests. Tin was precipitated from an aqua regia leachate with gaseous ammonia and gold was afterward recovered as metallic gold by reduction with sodium borohydride; silver was first precipitated as silver chloride from a nitric acid leachate and then reduced to metallic silver. Copper was selectively precipitated with oxalic acid from the solution coming from silver recovery and then recovered as metallic copper by means of a mild thermal treatment, without chemicals addition. The developed process allowed the recovery of gold, silver and copper in metallic form with yield and purity grade ≥ 98%.