Scrap computer keyboards a sustainable resource for silver (Ag) and low density oil (L D Oil)

Most neglected part of the scrap computers are the keyboards, which are generally incinerated by the informal recycling sectors creating environmental pollution and leads to the wastage of precious metallic contents present in it. Present paper is focused on a novel chemical processing technique developed to recover silver (Ag) as value added product and low density oil (L D Oil) from the computer keyboards. Initially, scrap keyboards were manually dismantled to separate Mylar sheets and the same were pyrolysed at 300 ◦C for 2 h to recover L D Oil. The obtained pyrolysed Mylar sheets was further crushed, milled and homogenized to reduce particle size (− 100 mesh). The crushed sample was leached using 2 M HNO3 at 60 ◦C in mixing time of 20 min and pulp density of 100 g/L to achieve maximum dissolution of Ag. The leaching kinetics for Ag dissolution well fitted with chemical reaction control dense constant size cylindrical particles, 1-(1-X)1/2 = kct. The obtained leach liquor was put to cementation process using metallic copper (Cu). Almost 99% of Ag gets cemented as Ag powder in 15 min at a constant solution temperature of 60 ◦C and pH 1.1. The developed bench scale process has application orientation to the industry after piloting the process

Separation of Cu, Sn, Pb from copper scrap coated with Sn and Pb

Tin/lead plating technologies have been used for unsurpassed solderability and in electrical and electronic equipments eliminating the potential for tin whisker formation. The present study is aimed at recovering of Cu, Sn, Pb, respectively, from the copper scrap coated with Pb and Sn. In the recycling process, tin was selectively leached from the scrap, and lead precipitated into PbCl2 powder. Because copper was not dissolved, so tin, lead, copper were recovered, respectively. The leaching tests were performed to investigate the effects of leaching conditions such as temperature, agitation speed, and oxidant concentration. In the process, the oxidant could be reused by electrical oxidation

Leaching behavior of valuable metals from by-product generated during purification of zinc electrolyte

Purification cake generated during cementation process contains valuable and hazardous metals such as cadmium, copper, zinc, lead, cobalt, nickel, and antimony. The purification cake has been dumped in landfill sites, and this could cause the environmental problem such as leak of leachate and the loss of valuable metal. The present study is aimed at investigating the leaching behaviors of metals in sulfuric acid solution to recover the valuable metals. The effects of reaction time, temperature, sulfuric acid concentration, agitation speed, pulp density were investigated to establish the leaching conditions. More than 99.9% of cadmium and zinc were leached within 5 min and same ratio of cobalt was leached within 30 min. Copper, nickel, and antimony were leached 99, 97, 95%, respectively, after 60 min. Lead was detected about 2% in 60 min in 1.0 M sulfuric acid at 50 °C and 400 rpm with 10 g/L pulp density for 180 min. It is possible that lead remains as a precipitate and cadmium, zinc, copper, cobalt, nickel, antimony in leach solution are recovered

Separation of Cu, Sn, Pb from photovoltaic ribbon by hydrochloric acid leaching with stannic ion followed by solvent extraction

A recycling process consisting of HCl leaching with Sn4 + followed by solvent extraction is proposed to recover Cu, Sn and Pb from photovoltaic (PV) ribbon. During HCl leaching with Sn4 +, Sn and Pb were removed from PV ribbon whereas Cu remained as plate. The leaching efficiency of Sn increased with increasing temperature, initial Sn4 + concentration or decreasing pulp density. In the case of leaching test performed in the 1 M HCl solution at 400 rpm and 70 °C with 5% pulp density and 5000 mg/L Sn4 +, the leaching efficiency of Sn increased to > 99% within 60 min, whereas 71.9% of Pb was recovered as PbCl2 powder after settling the leach solution for 24 h at room temperature. A solvent extraction with tri-butyl phosphate (TBP) was performed to extract selectively Sn from leach solution. The extraction efficiency of Sn increased with increasing the contents of TBP in kerosene, and < 1% of Pb was extracted. Therefore, the separation of Sn, Cu, Pb was achieved successfully by the recycling process

Regeneration of Sn4+ from Sn2+ solution during electrowinning process using anion exchange membrane

Electrowinning process to regenerate Sn4+from Sn2+in HCl solution using an electrowinning cell with anion exchange membrane was proposed to suggest a novel recycling process to recover Sn. During the tests, the effects of initial Sn2+concentration on the regeneration of Sn4+were investigated under the following condition; 7,000 mg/L, 10,000 mg/L, and 13,000 mg/L of Sn2+, 1 M HCl, 250 A/m2of current density, graphite anode, titanium cathode, room temperature, and 2 h. Electro-deposited Sn on the cathode showed dendritic structure regardless of the Sn2+concentration and no change of Sn concentration was observed in the anolyte. Leaching tests were performed using the anolyte, obtained from the electrowinning tests, to examine the amount of regenerated Sn4+concentration during electrowinning process. Based on the results of Sn leaching tests, it was found that 84.44%, 81.03%, and 79.43% of Sn4+were regenerated from 7,000 mg/L, 10,000 mg/L, 13,000 mg/L initial concentration of Sn2+solution, respectively. Consequently, it was found that the regeneration of Sn4+can occur during the electrowinning process at the same time with Sn recovery and Sn4+can be reused as an oxidant to leach Sn successfully

The removal of arsenic ion in electro-coagulation cell

The removal of As(V) and As(III) was investigated using electro-coagulation (EC) cell. Adsorption on hydro ferric oxide (HFO) generated by EC cell shows high ratio at lower pH and decreases with increasing pH. The removal efficiencies are higher in the feed solution with As(III) than with As(V). Total arsenic removal ratio is higher in the feed solution with As(III) than with As(V). Total arsenic removal ratios in EC process are over 90% at pH 4 to 9 at 1.0 A in the feed solution with As(III). At 0.5 A, As(III) adsorption ratio is 36.84% at pH 4 and total arsenic removal ratio is 60.79%, and As(III) adsorption ratio is 88.19% at pH 4 and total arsenic removal ratio is 91.13% at 1.0 A. High adsorption ratio of As(V) increases total arsenic removal ratio. In the EC cell, As(III) species could be oxidized to As(V) species, and high arsenic removal ratio is expected at low pH range by using EC process. The oxidation ratios of As(III) to As(V) are 7.1 to 41.3% and 11.1 to 27.7% at 0.5 A and 1.0 A, respectively. The EC process can oxidize As(III) to As(V), and As(V) has more affinity on HFO surface than As(III) at low pH ranges. This result suggest that this technology could be used to remove As ion from acid mine drainage. © 2011 Taylor & Francis Group, LLC

Dismantling of Electric and Electronic Components from Waste Printed Circuit Boards by Hydrochloric Acid Leaching with Stannic Ions

A dismantling process for separating electric and electronic components (EECs) from printed circuit board (PCB) was developed by using hydrochloric acid (HCl) leaching with stannic ions (Sn⁴⁺). The use of HCl solution with Sn⁴⁺ ions dissolves tin (Sn)-alloy solder that holds EECs on bare board, which allows the EECs to be detached from PCB. The feasibility of the new dismantling process was investigated by examining the effects of temperature, initial Sn⁴⁺ concentration and agitation speed on the dismantling of PCB. The effect of agitation speed was negligible and the dismantling-completion time was reduced rapidly with increasing temperature and initial Sn⁴⁺ concentration. The dismantling of PCB was completed within 30 min under the leaching conditions; HCl concentration, 1 mol/L; initial Sn⁴⁺ concentration, 13,000 mg/L; temperature, 90℃; and agitation speed, 300 rpm. Each metal was enriched after dismantling process; e.g. the content of Ag increased from 0.016% in PCB to 3.118% in registor. It was expected that efficient PCB recycling process could be designed to recover metals from EECs with higher concentrated metals

Leaching of tin from waste Pb-free solder in hydrochloric acid solution with stannic chloride

A hydrochloric acid (HCl) leaching process with stannic chloride (SnCl4) was proposed to leach Sn from waste Pb-free solder containing Sn, Ag, and Cu, where the oxidant stannic ion (Sn4 +) oxidizes Sn metal into stannous ion (Sn2 +). When Sn reagent-grade powder was leached in HCl solution with SnCl4, the leaching efficiency of Sn increased rapidly and the oxidation-reduction potential decreased with leaching time. In the leaching tests of Pb-free solder, the effect of factors such as the agitation speed, HCl concentration, pulp density, and temperature on the leaching behaviors of metals was investigated. The leaching efficiencies of Sn increased rapidly in the beginning of leaching with increasing agitation speed, HCl concentration, and temperature. The difference in the leaching efficiencies was negligible after 90 min under the following conditions: HCl concentration of 1–3 kmol m- 3, agitation speed of 300–600 rpm, and temperature of 50 °C or 70 °C. Although the pulp density was increased from 1% to 2%, the Sn concentration dissolved did not exceed 10,500 g m- 3 because of the lack of oxidant, and the increase in the initial concentration of Sn4 + as the oxidant could accelerate the leaching of Sn. A Sn leaching efficiency of greater than 99% was achieved in 1 kmol m- 3 HCl with 10,000 g m- 3 Sn4 + at 400 rpm and 50 °C with 1% pulp density within 90 min. Ag was not detected in any of the leaching tests. Although the leaching solution contained 24.5 g m- 3 of Cu, the addition of Sn powder was successful in removing Cu from the solution via a cementation reaction. Thus, a Sn leaching solution was successfully obtained from Pb-free solder via HCl leaching with SnCl4

The effect of temperature on the leaching of monazite obtained from heavy mineral sands

Pressure leaching, electrogenerated chlorine leaching and concentrated sulfuric acid leaching were performed to investigate the leaching behavior of monazite concentrate with various temperature ranges. The pressure leaching was tested at 5 atm and 220°C and the concentrations of Ce and La increase with increasing sulfuric acid concentration from 0.01 mol/L to 1 mol/L and decreasing the particle size of monazite concentrate from -200 mesh - + 325 mesh to -325 mesh. In the electrogenerated chlorine leaching system, the concentration of La decreases with increasing temperature from 30°C to 70°C, which resulted from a decrease in solubility of chlorine with increasing temperature. In the concentrated sulfuric acid leaching system, the leaching ratios of La and Nd increase to over 99% with increasing temperature to 220°C. The higher metal concentration of Ce, La and Nd are obtained in the concentrated sulfuric acid leaching system than in the pressure leaching and the electrogenerated chlorine leaching system. This result suggests that higher temperature and concentration of sulfuric acid could accelerate the dissolution of monazite concentrate

Leaching of zinc from contaminated soil using citrate

A citric acid leaching test after heavy medium separation process was performed to remove the heavy metal contaminat such as Pb, Cu, and Zn from contaminated soil. The lead component was removed from soil by heavy medium separation whereas zinc component shows 0% - 37.9% removal ratio with particle size. The citric acid leaching was conducted to remove the remained zinc component. The removal ratio of Zn reached to more than 95% under the conditions; 10% in pulp density, 200 rpm in agitation speed, 50 °C, 2 mol/L in citric acid concentration at 2 hrs in leaching time. These results suggest that the heavy medium separation method followed by citric acid leaching is effective for treatment of soil contaminated with various chemical forms of heavy metal