Leaching of low grade zinc oxide ores in Ida^(2-)-H_2O system

Ida2--H2O system（iminodiacetate aqueous solution） was used to leach a low grade zinc oxide ore for Zn extraction.The effects of leaching time,liquid-solid ratio（L/S）,total concentration of Ida2-（[Ida2-]T）,leaching temperature and pH on Zn leaching recovery and the dissolution of impurities such as Ca,Mg,Cu,Ni,Fe,Pb and Cd were investigated.Results show that Ca,Mg and Fe in ores were hardly dissolved in alkalescent iminodiacetate aqueous solution,while valuable metals such as Cu,Ni,Pb and Cd were partly dissolved into leaching liquor with Zn.The recovery of Zn reaches 76.6% when the ores were leached for 4 h at 70 ℃ by 0.9 mol/L iminodiacetate aqueous solution with pH of 8 and L/S of 5：1.

Reaction mechanism of fluoride conversion into BF^(4-) during sulphuric acid leaching of roasted bastnaesite

The bastnaesite used in hydrometallurgy usually contains 7%-11% fluorine,and the conversion of fluorine into high-value products is the key to achieving green production of rare earths and improving the comprehensive utilization of bastnaesite.In order to recover fluorine from bastnaesite in the form of KBF4,the mechanism of F^(-)conversion to BF^(4-)in sulphuric acid leaching solution of roasted bastnaesite was studied by using Eh-pH diagram and simulation experiment.It shows that the formation of BF^(4-)is affected by pH in the absence of rare earths.BF^(4-)is hydrolyzed to BF3 OH-and F-when the pH is greater than 3.9,and part of F-exists as HF^(2-)when pH is lower than 2.In the presence of La^(3+),the formation of BF^(4-)is mainly affected by LaF_(3) when pH is greater than 0,and in the case that the pH is lower than 2,it is mainly affected by HF^(2-).When Ce4+is present in solution,CeF_(2)^(2+) can exist stably in sulphuric acid solution.Bringing down the pH can reduce the stability of CeF_(2)^(2+) and increase the BF^(4-)conversion rate.Based on these results,KBF4 was prepared in the alkaline solution of bastnaesite,and the conversion of BF^(4-)is 84.31%.This provides a theoretical basis for the recovery of fluorine from bastnaesite in the form of KBF_(4).

老挝万象平原钾镁盐矿溶浸试验研究

在实验室建立了一套溶浸试验装置。以水为浸出剂，通过测定60℃、90℃、100℃时浸出液中KCl、NaCl、MgCl：组成浓度随时间的变化，考察老挝万象钾镁盐矿在水中的溶解行为，得到60℃、90℃、100℃条件下钾镁盐矿中KCl在水中的平衡浓度（质量百分含量）分别为5．73％、6．90％、7．93％。浸出液中KCl平衡浓度随温度的升高而增大。试验结果对老挝万象钾镁盐矿资源的开发利用具有理论参考和实际应用价值。

广东厚婆坳锡床形成条件的实验模拟

在对厚婆坳锡床进行了较为系统的基础地质和矿物中流体包裹体研究的基础上,笔者选择一些对解决矿床成因起重要作用的方面进行了高温高压实验模拟工作。研究表明,在有利的成矿溶液作用下,沉积岩中锡的活化率可高达30％,亚锡氯络合物是本矿床锡的主要迁移形式。此外,笔者成功地模拟成矿条件,在350℃、500atm及与Ni—NiO缓冲剂相近的氧逸度下,用二氯化锡合成出了锡石。

Nitrogen cycling and environmental impacts in upland agricultural soils in North China： A review

The upland agricultural soils in North China are distributed north of a line between the Kunlun Mountains, the Qinling Mountains and the Huaihe River. They occur in arid, semi-arid and semi-humid regions and crop production often depends on rain-fed or irrigation to supplement rainfall. This paper summarizes the characteristics of gross nitrogen（N） transformation, the fate of N fertilizer and soil N as well as the N loss pathway, and makes suggestions for proper N management in the region. The soils of the region are characterized by strong N mineralization and nitrification, and weak immobilization and denitrification ability, which lead to the production and accumulation of nitrate in the soil profile. Large amounts of accumulated nitrate have been observed in the vadose-zone in soils due to excess N fertilization in the past three decades, and this nitrate is subject to occasional leaching which leads to groundwater nitrate contamination. Under farmer＇s conventional high N fertilization practice in the winter wheat-summer maize rotation system（N application rate was approximately 600 kg ha–1 yr–1）, crop N uptake, soil residual N, NH_3 volatilization, NO_3~– leaching, and denitrification loss accounted for around 27, 30, 23, 18 and 2% of the applied fertilizer N, respectively. NH_3 volatilization and NO_3~– leaching were the most important N loss pathways while soil residual N was an important fate of N fertilizer for replenishing soil N depletion from crop production. The upland agricultural soils in North China are a large source of N_2O and total emissions in this region make up a large proportion（approximately 54%） of Chinese cropland N_2O emissions. The “non-coupled strong ammonia oxidation” process is an important mechanism of N_2O production. Slowing down ammonia oxidation after ammonium-N fertilizer or urea application and avoiding transient high soil NH4＋ concentrations are key measures for reducing N_2O emissions in this region. Further N management should aim to minimize N losses from crop and livestock production, and increase the recycling of manure and straw back to cropland. We also recommend adoption of the 4 R（Right soure, Right rate, Right time, Right place） fertilization techniques to realize proper N fertilizer management, and improving application methods or modifying fertilizer types to reduce NH_3 volatilization, improving water management to reduce NO_3~– leaching, and controlling the strong ammonia oxidation process to abate N_2O emission. Future research should focus on the study of the trade-off effects among different N loss pathways under different N application methods or fertilizer products.