Mobile Phone Printed Circuit Boards Research Articles

Selective recovery of gold from waste mobile phone PCBs by hydrometallurgical process

The leaching of gold from the scrap mobile phone PCBs by electro-generated chlorine as an oxidant and its recovery by ion exchange process was investigated. The leaching experiments were carried out by employing separate leaching reactor connected with the anode compartment of a Cl 2 gas generator. The leaching of gold increased with increase in temperature and initial concentration of chlorine, and was favorable even at low concentration of acid, whereas copper leaching increased with increase in concentration of acid and decrease in temperature. In a two-stage leaching process, copper was mostly dissolved (97%) in 165 min at 25 °C during the 1st stage leaching in 2.0 mol/L HCl by electro-generated chlorine at a current density of 714 A/m 2 along with a minor recovery of gold (5%). In the 2nd stage gold was mostly leached out (93% recovery, ∼67 mg/L) from the residue of the 1st stage by the electro-generated chlorine in 0.1 mol/L HCl. Gold recovery from the leach liquor by ion exchange using Amberlite XAD-7HP resin was found to be 95% with the maximum amount of gold adsorbed as 46.03 mg/g resin. A concentrated gold solution, 6034 mg/L with 99.9% purity was obtained in the ion exchange process.

Bioleaching of gold and copper from waste mobile phone PCBs by using a cyanogenic bacterium

Chromobacterium violaceum ( C. violaceum), a cyanide generating bacterium has been used to leach out gold and copper from the waste mobile phone printed circuit boards (PCBs) containing ∼34.5% Cu and 0.025% Au in YP (yeast extract and polypeptone with glycine) medium. The bioleaching was carried out in an incubator shaker (150 rpm) at 30 °C and 15 g/L pulp density in the pH range 8–11. Dissolution of gold and copper increased from 7.78% (0.225 ppm) to 10.8% (0.46 ppm) and 4.9% (419 ppm) to 11.4% (879 ppm) in 8 days with increase in pH from 8 to 11 and 8 to 10 respectively. Supplementing oxygen with 0.004% ( v/ v) H 2O 2 increased the copper leaching to 24.6% (1743 ppm) at pH 10 in 8 days whereas improvement in gold leaching was insignificant with the recovery of 11.31% Au at pH 11.0. The waste PCBs can thus be recycled in environmental friendly manner.

Bacterial Cyanide Generation in the Presence of Metal Ions (Na+, Mg2+, Fe2+, Pb2+) and Gold Bioleaching from Waste PCBs

As an alternative using cyanide chemicals for gold extraction, the application of a cyanogenic bacterium viz. Chromobacterium violaceum (C. violaceum) in YP medium has been investigated. The catalytic roles of metal ions such as Na+, Mg2+, Fe2+, and Pb2+, as well as the effect of Na2HPO4 nutrient addition on the cyanide generation efficiency of the bacterium in this medium have been elucidated. While MgSO4 and FeSO4 added to the medium were equally effective for cyanide generation, improved efficiency was obtained in the presence of Na2HPO4 and Pb(NO3)2. In order to examine the effectiveness of C. violaceum cultured in YP medium for the generation of cyanide ions, the dissolution of gold and copper from waste mobile phone printed circuit boards (PCBs), a good source of gold and copper in alkaline conditions, was tested at 30°C, for various pH values and metal ion contents. Gold leaching was found to be 11% in 8 d at pH 11.0 in presence of 4.0 × 10−3 mol/L MgSO4, whereas; copper recovery was high (11.4%) at pH 10.0. Addition of 1.0 × 10−2 mol/L Na2HPO4 and 3.0 × 10−6 mol/L Pb(NO3)2 to the YP medium increased copper leaching to 30.3% and 38.1%, respectively, at pH 10.0 in 8 d. However, this effect was not observed for gold leaching.

Thiosulfate leaching of gold from waste mobile phones

The present communication deals with the leaching of gold from the printed circuit boards (PCBs) of waste mobile phones using an effective and less hazardous system, i.e., a copper-ammonia-thiosulfate solution, as an alternative to the conventional and toxic cyanide leaching of gold. The influence of thiosulfate, ammonia and copper sulfate concentrations on the leaching of gold from PCBs of waste mobile phones was investigated. Gold extraction was found to be enhanced with solutions containing 15-20 mM cupric, 0.1-0.14 M thiosulfate, and 0.2-0.3 M ammonia. Similar trends were obtained for the leaching of gold from two different types of scraps and PCBs of waste mobile phones. From the scrap samples, 98% of the gold was leached out using a solution containing 20 mM copper, 0.12 M thiosulfate and 0.2 M ammonia. Similarly, the leaching of gold from the PCBs samples was also found to be good, but it was lower than that of scrap samples in similar experimental conditions. In this case, only 90% of the gold was leached, even with a contact time of 10h. The obtained data will be useful for the development of processes for the recycling of gold from waste mobile phones.

ＷＥＥＥ中の金属リサイクルに関する研究―金属含有量インベントリ作成のための調査 ２―

Although Cu, Ag, Au and other metals are used for the electrical and electronic equipment (EEE) , the many kinds of metals in WEEE (Waste EEE) are not recycled now except Cu and precious metals. It is desired to promote recycling of metals in WEEE. However, EEE is improved with a time and the components and their materials which are used for EEE also change. That is, it means that the quality of recycling resources changes in recycling of WEEE. In this paper, it aimed at creating those inventories as basic information on examination of the recycling system of WEEE. The change of the mobile phone unit by improvement such as a miniaturization and introduction of a new function is quicker than other EEE. Therefore, contents of each element in mobile phone's PCB (Printed Circuit Board) manufactured in 1997, 2002-2003 and 2005-2006 were investigated, and the causes of some changes were considered. It was shown that Pd's substitution material (Ni) and tantalum capacitor's substitute device (ceramic capacitor) have spread, and the amount of Pd and Ta used is decreasing by the unstable supply of metal resources or their rising value. It was shown that the amount of the harmful elements, such as Pb, Sb, Br, is decreasing by new substance regulation and growing environment-conscious. Moreover, some points in the recycling system which should be taken into consideration were clarified.

ＷＥＥＥ中の金属リサイクルに関する研究―金属含有量インベントリ作成のための調査―

Although Cu, Ag, Au and other metals are used for the electrical and electronic equipment (EEE) , the many kinds of metals in WEEE (Waste EEE) are not recycled now except Cu and precious metals. It is desired to promote recycling of metals in WEEE. However, EEE is improved with a time and the components and their materials which are used for EEE also change. That is, it means that the quality of recycling resources changes in recycling of WEEE. In this paper, it aimed at creating those inventories as basic information on examination of the recycling system of WEEE. The change of the mobile phone unit by improvement such as a miniaturization and introduction of a new function is quicker than other EEE. Therefore, contents of each element in mobile phone's PCB (Printed Circuit Board) manufactured in 1997, 2002-2003 and 2005-2006 were investigated, and the causes of some changes were considered. It was shown that Pd's substitution material (Ni) and tantalum capacitor's substitute device (ceramic capacitor) have spread, and the amount of Pd and Ta used is decreasing by the unstable supply of metal resources or their rising value. It was shown that the amount of the harmful elements, such as Pb, Sb, Br, is decreasing by new substance regulation and growing environment-conscious. Moreover, some points in the recycling system which should be taken into consideration were clarified.

Development and validation of a lead-free alloy for solder paste applications

A lead-free solder alloy has been developed and, in form of a solder paste, validated for use in the assembly of surface mount printed circuit boards (PCB). Liquidus and solidus temperatures have been measured by thermal analysis and an optimum composition selected. Wetting balance tests have been done comparing the performance of the alloy with that of 60/40 tin/lead (SnPb), 99/1 tin/copper (SnCu) and 96.5/3.5 tin/silver (SnAg) alloys on bare copper (Cu) coupons. The tests showed faster wetting for the alloy than for the SnAg and SnCu alloys, with results under some conditions comparable to those achieved with 60/40 SnPb. A no-clean rosin base solder paste was made up with the alloy and used to assemble 20 standard mobile phone PCBs. The boards were successfully soldered by nominally raising the reflow temperature, but only by 10/spl deg/C as compared with eutectic SnPb pastes. Solder joint reliability was tested by temperature cycling Pb-free and 63/37 soldered boards between -25/spl deg/C and +125/spl deg/C for 1000 cycles. Results as assessed by metallographic analysis were better for the Pb-free alloy than for the reference SnPb alloy.