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A tannin-based novel adsorbent, named "BTU-PT gel", was prepared by immobilizing bisthiourea (BTU) ligand on persimmon tannin (PT) extract. The adsorption behaviors of precious metal ions along with other coexisting base metal ions onto BTU-PT gel were studied by batch and continuous column methods. The gel exhibited remarkable selectivity for precious metal ions such as Au(III), Pd(II), and Pt(IV) over base metal ions such as Cu(II), Fe(III), Ni(II), and Zn(II) in 1−5 mol dm −3 hydrochloric acid. The adsorption of precious metal ions on the present gel was found to obey the typical monolayer type of Langmuir model, and the maximum adsorption capacity of the adsorbent was evaluated as 5.18 mol kg −1 for Au(III), 1.80 mol kg −1 for Pd(II), and 0.67 mol kg −1 for Pt(IV). Combination of ion exchange, electrostatic interaction, and coordination through the thiocarbonyl group is the mechanism of adsorption of precious metals on BTU-PT gel. In the case of Au(III) adsorption, the adsorbed species was simultaneously reduced to elemental gold by abundant polyphenolic groups of the tannin matrix. Elution by using acidothiourea solution in continuous column experiment recovered the adsorbed precious metals almost quantitatively. The results of a potential reusability test of the gel for consecutive adsorption and elution cycles by continuous column experiment indicated that the gel was stable and regenerated with undiminished metal uptake capacity up to five cycles. The real time applicability of the adsorbent for the recovery of precious metals from real industrial liquor was evaluated from actual acidic leach liquor of printed circuit boards of spent mobile phones. The gel selectively adsorbed precious metal species but exhibited negligible affinity toward base metals present in the leach liquor. The BTU-PT gel is a potential adsorbent for selective recovery of precious metals from acidic leachate of spent mobile phones containing elevated concentrations of base metals.

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BackgroundNepal is a key supplier of labour for countries in the Middle East, India and Malaysia. As many more men than women leave Nepal to work abroad, female migrant workers are a minority and very much under-researched. The aim of the study was to explore the health problems of female Nepalese migrants working in the Middle-East and Malaysia.MethodsThe study was conducted among 1010 women who were registered as migrant returnees at an organisation called Pourakhi Nepal. Secondary data were extracted from the records of the organisation covering the five-year period of July 2009 to July 2014.ResultsThe 1010 participants were aged 14 to 51 with a median age of 31 (IQR: 38-25) years. A quarter of respondents (24%) reported having experienced health problems while in the country of employment. Fever, severe illness and accidents were the most common health problems reported. Working for unlimited periods of time and not being able to change one’s place of work were independently associated with a greater likelihood of health problems. Logistic regression shows that migrant women who are illiterate [OR = 1.56, 95% CI: 1.02 to 2.38, p = 0.042], who had changed their workplace [OR = 1.63, 95% CI: 1.14 to 2.32, p = 0.007], who worked unlimited periods of time [OR = 1.64, 95% CI: 1.44 to 1.93, p = 0.020], had been severely maltreated or tortured in the workplace [OR = 1.84, 95% CI: 1.15 to 2.92, p = 0.010], were not being paid on time [OR = 2.38, 95% CI: 1.60 to 3.55, p = 0.038] and migrant women who had family problems at home [OR = 3.48, CI 95%: 1.22 to 9.98, p = 0.020] were significantly associated with health problems in their host country in the Middle East.ConclusionFemale migrant workers face various work-related health risks, which are often related to exploitation. The Government of Nepal should initiate awareness campaigns about health risks and rights in relation to health care services in the host countries. Recruiting agencies/employers should provide information on health risks and training for preventive measures. Raising awareness among female migrant workers can make a change in their working lives.Electronic supplementary materialThe online version of this article (10.1186/s12914-018-0145-7) contains supplementary material, which is available to authorized users.

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