Microbial nitrification and acidification of lacustrine sediments deduced from the nature of a sedimentary kaolin deposit in central Japan

Kaolin deposits in the Seto-Tono district, central Japan, were formed by intense kaolinization of lacustrine arkose sediments deposited in small and shallow inland lakes in the late Miocene. Based on mineralogical and stable isotopic (Fe, C, N) studies of Motoyama kaolin deposit in the Seto area, we concluded that it was formed by microbial nitrification and acidification of lacustrine sediments underneath an inland lake. Small amounts of Fe–Ti oxides and Fe-hydroxide in the kaolin clay indicated that iron was oxidized and leached during the kaolinization. The field occurrences indicate that leached ferric iron precipitated on the bottom of the kaolin deposit as limonite crusts, and their significantly fractionated Fe isotope compositions suggest the involvement of microbial activity. The C/N ratios of most of the kaolin clay are distinctly higher than those of modern lacustrine sediment. Although, the possibility of a low-temperature hydrothermal origin of the kaolin deposit cannot be completely ruled out, it is more likely that acidification by dilute nitric acid formed from plant-derived ammonia could have caused the kaolinization, Fe oxidation and leaching. The nitrate-dependent microbial Fe oxidation is consistent with dilute nitric acid being the predominant oxidant.

Study on Technological Process Innovation of Non-Cyanide Leaching

Nowadays, there are many gold leaching processes, and the dominant one is cyanidation, but the virulence of cyanidation seriously endangers the environment and human health. In order to reduce environmental pollution and improve the recovery rate of gold, metallurgical workers put forward a variety of new gold leaching methods, which can be roughly divided into two types: one is to develop pretreatment technology on the basis of traditional cyanidation method; The other is non-cyanide leaching of gold. Based on the existing Non-Cyanide leaching technology, this paper puts forward the process innovation of Non-Cyanide leaching technology, thiourea method and dilute nitric acid pre-oxidation treatment process. The thiourea non-cyanide leaching system was investigated. According to the leaching situation of gold and silver in raw ore, the innovative scheme of gold and silver leaching technology was selected. Compared with other treatment methods, thiourea method and dilute nitric acid pre-oxidation treatment technology overcome the danger of high pressure, and the nitrogen oxide gas produced in the dilute nitric acid oxidation process can be recycled, which basically does not pollute the environment.

Preliminary Study of Heavy Metals in Low-Cost Jewelry Items Available in Nigerian Markets

Background Many developing countries either lack or have weakly enforced regulations on imported goods. A high percentage of low-cost jewelry items in Nigeria are imported from abroad. There is concern about the levels of heavy metals present in these products. Objectives The present study examined the levels of lead (Pb), cadmium (Cd), chromium (Cr) and nickel (Ni) in inexpensive jewelry purchased from retail wholesale shops in Ibadan metropolis, southwestern Nigeria. Methods One hundred (100) assorted jewelry items were digested in dilute nitric acid solution followed by atomic absorption spectrophotometric analysis. Results Out of the total number of jewelry items analyzed, 12% of them had Pb concentrations above European Union (EU) safety limits. Also, 63%, 42% and 62% of items had Cd, Cr and Ni average concentrations above their EU limits. Notably, 3%, 27% and 8% of the items had Pb, Cd and Cr concentrations over 103 times above their EU limits Overall, Cd showed the highest average level in rings (256,952 mg/kg) followed by bracelets (60,627 mg/kg) and earrings (54,388 mg/kg). All metals in solid bangles were within their EU guidelines. Conclusions Given the significant deleterious impacts of these metals on human health, low-cost jewelry poses a serious potential threat to users' health. Policies to guarantee the safety of low-cost jewelry items must be established and enforced. Competing Interests The authors declare no competing financial interests.

Pengendapan Torium (Th) dari Monasit Bangka Setelah Proses Solvent Impregnated Resin (SIR)

ABSTRAKPengolahan monasit Bangka secara basa dilakukan melalui tahapan dekomposisi; pelarutan parsial pH 3,7; pengendapan parsial pH 6,3; dan pengendapan total pH 9,8. Proses tersebut menghasilkan natrium fosfat, Rare Earth (RE) hidroksida, uranium (U), dan torium (Th). Pada proses dekomposisi, 99 % natrium fosfat telah terambil dan RE hidroksida telah terpisah dari U dan Th dengan recovery 85 %. Sementara itu, U dan Th yang dihasilkan masih bercampur sehingga perlu dipisahkan. Pemurnian Th dari U pada monasit telah dilakukan dengan metode Solvent Impregnated Resin (SIR) dan dilanjutkan dengan proses elusi setelah SIR. Hasilnya, Th masih berada pada fase cairan berupa larutan torium nitrat [Th(NO3)2] sehingga perlu diendapkan sebagai torium hidroksida [Th(OH)2] untuk memudahkan proses berikutnya. Pengendapan Th setelah proses SIR dilakukan dengan tujuan memperoleh kondisi optimum pengendapan. Resin penyokong yang digunakan adalah amberlite XAD-16 menggunakan ekstraktan yang diimpregnasikan dengan tributyl phosphate (TBP), reagen elusi asam nitrat (HNO3) encer dan reagen pengendapan amoniak (NH4OH). Parameter yang diteliti adalah pengaruh pH dan waktu pengendapan terhadap recovery Th. Hasil penelitian menunjukkan kondisi optimum pengendapan Th dari monasit setelah proses SIR pada pH 1,2 dan waktu 60 menit dengan recovery 84,74 % Th; 3,26 % U; 34,74 % RE; dan 8,52 % PO4.ABSTRACTAlkaline processing of Bangka monazite is carried out through stages like decomposition; partial dissolution pH 3.7; partial precipitation pH 6.3; and total precipitation pH 9.8. These procesess produce sodium phosphate, Rare Earth (RE) Hydroxide, uranium (U), and thorium (Th). On decomposition procsess, 99 % of sodium phosphate had been recovered and RE Hydroxide was separated from U and Th with 85% recovery. Meanwhile, the U and Th products were still mixed so that needs to separate. Purification of Th from U in monazite had been carried out by using Solvent Impregnated Resin (SIR) method and continued by elution after SIR. The result is that Th is still in the liquid phase as thorium nitrate [Th(NO3)2] solution so it needs to be precipitated as thorium hydroxide [Th(OH)2] to facilitate the next process. Precipitation of Th after SIR process is conducted with the aim to obtain optimum precipitation condition. The supporting resin used is amberlite XAD-16 with impregnated tributyl phosphate (TBP) extractant, dilute nitric acid (HNO3) as elution reagent, and ammonium hydroxide (NH4OH) as precipitation reagent. The observed parameters are the effect of pH and precipitation time on Th recovery. The results show that the optimum precipitation conditions of Th from monazite after SIR process is on pH 1.2 and 60 minutes time, resulting recovery of 84.74 % Th, 3.26 % U, 34,74 % RE, and 8.52 % PO4.