简介概要

Molybdenum recovery from oxygen pressure water leaching residue of Ni-Mo ore

来源期刊：Rare Metals2013年第2期

论文作者：Ming-Shuang Wang Chang Wei Gang Fan Zhi-Gan Deng Si-Fu Wang Jun Wu

文章页码：208 - 212

摘要：This article investigated molybdenum recovery from oxygen pressure water leaching residue of Ni-Mo ore using alkaline leaching, followed by chemical treatment of leach liquor. Parameters affecting Mo leaching rate, such as sodium hydroxide concentration, reaction time, a liquid-to-solid ratio, and temperature for the preliminary alkaline leaching were experimentally determined. The results showed that more than 88% of molybdenum was leached under the optimum conditions （2.5 ml·g-1 NaOH, 80 °C, a liquid to solid ratio 3 ml·g-1 , and reaction time 3 h）. After the purification of leach liquor, a CaMoO 4 product of 99.2% purity could be obtained by CaCl 2 precipitation method. The whole Mo recovery reached about 82.7%.

Rare Metals 2013,32(02),208-212+2

Molybdenum recovery from oxygen pressure water leaching residue of Ni-Mo ore

Ming-Shuang Wang Chang Wei Gang Fan Zhi-Gan Deng Si-Fu Wang Jun Wu

Faculty of Metallurgical and Energy Engineering,Kunming University of Science and Technology

作者简介：Ming-Shuang Wang e-mail:wms110220@163.com;Chang Wei e-mail:weichang502@sina.cn;

收稿日期：22 February 2012

基金：supported by the National High Technology Research and Development Program of China(No.2009AA06Z106);Yunnan Provincial Science and Technology Department of China(No.2011GA004);

Molybdenum recovery from oxygen pressure water leaching residue of Ni-Mo ore

Abstract：

This article investigated molybdenum recovery from oxygen pressure water leaching residue of Ni-Mo ore using alkaline leaching, followed by chemical treatment of leach liquor. Parameters affecting Mo leaching rate, such as sodium hydroxide concentration, reaction time, a liquid-to-solid ratio, and temperature for the preliminary alkaline leaching were experimentally determined. The results showed that more than 88% of molybdenum was leached under the optimum conditions (2.5 ml·g-1 NaOH, 80 °C, a liquid to solid ratio 3 ml·g-1 , and reaction time 3 h). After the purification of leach liquor, a CaMoO 4 product of 99.2% purity could be obtained by CaCl 2 precipitation method. The whole Mo recovery reached about 82.7%.

Keyword：

Mo recovery; Residue; Alkaline leaching; Calcium molybdate;

Received： 22 February 2012

1 Introduction

Molybdenum is an essential trace element for both animals and plant[1].Also,molybdenum is a transition metal that has wide applications in manufacturing electronic parts,a variety of glass,ceramic,lubricant,and dyes;in production of catalyst and pigment;and in alloying the steels[2–4].

Primary sources for molybdenum recovery mainly come from molybdenite,wulfenite,powellite,by-product of copper smelting,as well as spent catalyst in the world.However,with the ceaseless exploitation of minerals and the rising prices of molybdenum products,these primary sources are insufficient to supply demand,and many countries begin to pay much attention to the low-grade ores.In southern China,considerable reserves of Ni–Mo ore have been found successively in Guizhou,Hunan,Hubei,Yunnan,and Zhejiang provinces since the 1960s[5].Ni–Mo ore is a carbonaceous shale that contains 0.35%–8.17%molybdenum in the form of MoS₂,and 0.73%–7.03%nickel in the form of NiS₂,Ni₃S₄,NiS,or NiAsS[6].In recent years,several processes have been proposed for Mo recovery from Ni–Mo ore:Na₂CO₃calcination–water leaching,oxidation roasting–NaClO leaching,electric-oxidation,and NaOH?NaClO leaching with mechanical activation[7–10].These processes are effective to recover molybdenum,while suffering from either energyintensive or high reagent cost.In addition,nickel concentrated on the residue needs to be further recovered.Considering that nickel is also an important valuable metal,Wang[11]have reported using oxidation–sulfation roasting–water leaching to treat Ni–Mo ore.However,this process has drawbacks resulting in harmful SO₂pollution and multilevel processing.Chen et al.[12]have studied eco-friendly bioleaching to recover nickel and molybdenum from Ni–Mo ore in a membrane biological reactor.Nevertheless,the recovery of metals was very low.In our previous study,oxygen pressure water leaching was found to be suitable for low-grade Ni–Mo ore.About 97%of nickel and 70%of molybdenum were recovered as NiSO₄and MoO₂SO₄,respectively,under the optimum conditions:oxygen pressure of 1.2 MPa,a liquidto-solid ratio(L/S)of 2 ml?g^-1,leaching temperature of150°C,and a reaction time of 5 h.

Unfortunately,a mass of residues containing about 2.9%–3.5%of molybdenum were produced in the oxygen pressure water leaching process.The toxicity of molybdenum in humans is considered to be low,but hyperuricemia and goutlike symptoms have been found among workers exposed to molybdenum in a copper–molybdenum plant,as well as among the general population living in an area with high molybdenum and copper contents in soil and vegetables[13,14].For comprehensive utilization of resource and avoiding the negative effect of molybdenum on human health,the oxygen pressure water leaching residue of Ni–Mo ore can be considered as a secondary source for molybdenum recovery.

The aim of this article was to recover molybdenum from oxygen pressure water leaching residue of Ni–Mo ore.The parameters affecting Mo leaching rate,such as sodium hydroxide concentration,reaction time,L/S,and temperature were systematically investigated.The purification of leach liquor and production of calcium molybdate were also investigated thereafter.

2 Materials and methods

2.1 Materials

The Ni–Mo ore collected from Guizhou province was processed by oxygen pressure water leaching.The residue was dried at 75°C and subsequently ground.The chemical composition of the residue is listed in Table 1.The major phases identified by XRD analysis were quartz,anhydrite,molybdenum oxide,and ferrous sulfide,as shown in Fig.1.Analytic grade reagents including NaOH,H₂O₂,MgCl₂,and CaCl₂were used in this study.All aqueous solutions were prepared using distilled water.

2.2 Methods

A three-neck flask of 500-mL capacity was used in the alkaline leaching process.The flask was provided with a magnetic stirrer installed through the central neck,and athermometer and a baffle inserted into the flask through the other two necks.The flask was immersed in a thermostatic water bath,and the temperature of the system was maintained at a specific value.Sodium hydroxide solution prepared was charged to the flask and heated to the required temperature.100 g of residue was added into the alkaline medium,and the stirring speed was kept at a constant300 r?min^-1for all leaching experiments.After the required reaction time,the insoluble solid was separated from the slurry by vacuum filtration,and the filter cake was submitted to two successive rinsing steps using distilled water(at the same L/S of 3 ml?g^-1;each rinsing step lasted for 30 min at 80°C followed by filtration).The leach liquor was analyzed by ICP-AES for its molybdenum,silicon,phosphorus,and arsenic content.Impurities removal from leach liquor was carried out by adding MgCl₂in the presence of H₂O₂.Molybdenum recovery from the leach solution was performed by CaCl₂precipitation method.The product of CaMoO₄was dried at 70°C.

Table 1 Chemical composition of oxygen pressure water leaching residue of Ni–Mo ore 下载原图

Table 1 Chemical composition of oxygen pressure water leaching residue of Ni–Mo ore

Fig.1 XRD pattern of oxygen pressure water leaching residue of Ni–Mo ore

3 Results and discussion

3.1 Alkaline leaching

3.1.1 Effect of sodium hydroxide concentration

Figure 2 illustrates the effect of sodium hydroxide concentration from 1 to 3 mol?L^-1on Mo leaching rate.It was found that Mo leaching rate increased with increasing sodium hydroxide concentration up to a maximum of88.11%leaching rate at sodium hydroxide concentration of 2.5 mol?L^-1and then decreased with a further increase in sodium hydroxide concentration.The main chemical reactions during leaching can be described as follows:

Fig.2 Effect of sodium hydroxide concentration on Mo leaching rate at 80°C with a liquid to solid ratio of 3 ml?g-1for 3 h

For the decrease of Mo leaching rate at 3 mol?L^-1sodium hydroxide,it may be explained that Fe(OH)₂turned to Fe(OH)₃gel,which adsorbed molybdenum in situ precipitation.Taking into account the production cost,2.5 mol?L^-1of sodium hydroxide concentration in this study was advisable.

3.1.2 Effect of reaction time

The effect of reaction time on the Mo leaching rate was studied in the range from 1 to 5 h.As shown in Fig.3,prolonging the reaction time was beneficial to Mo leaching rate.Mo leaching rate increased gradually from 76.86%to88.15%with an increase in reaction time from 1 to 3 h.This indicated that the reaction speed was very fast before3 h.However,a further increase in reaction time did not significantly affect Mo leaching rate.Therefore,the reaction time was kept to 3 h in subsequent experiments.

3.1.3 Effect of liquid-to-solid ratio

A series of five experiments were carried out by varying L/S ranging from 1.5 to 3.5 ml?g^-1.It can be seen in Fig.4that Mo leaching rate increased with increasing the L/S.In fact,improving the L/S was favorable for the diffusion and mass transfer,whereas Mo leaching rate at the L/S of3.5 ml?g^-1was close to that at the L/S of 3 ml?g^-1.Hence,the L/S of 3 ml?g^-1in the following leaching experiments was chosen.

Fig.3 Effect of reaction time on Mo leaching rate using 2.5 mol?L-1sodium hydroxide at 80°C with a liquid to solid ratio of 3 ml?g-1

Fig.4 Effect of liquid to solid ratio on Mo leaching rate using2.5 mol?L-1sodium hydroxide at 80°C for 3 h

3.1.4 Effect of temperature

The effect of temperature on the Mo leaching rate was studied by performing experiments at 25,40,60,80,and90°C.As can be seen in Fig.5,Mo leaching rate increased gradually with increase in temperature from 25 to 80°Cand then decreased with a further increase in temperature.In addition,Mo leaching rate at 40°C approximated to that of 90°C,which was around 85%.The explanation for this phenomenon may be described as follows:on the one hand,the residue is discomposed difficultly at the lower temperature range(25–60°C),while the subsequent rinsing steps were carried out at 80°C,which provided advantageous dynamic conditions for Mo leaching rate;on the other hand,the slurry became sticky at 90°C due to waterevaporation loss,which hindered the diffusion of molybdenum.The maximum Mo leaching rate still reached around 89.03%at 80°C.As a consequence,80°C was chosen as the optimum temperature.

Fig.5 Effect of temperature on Mo leaching rate using 2.5 mol?L-1sodium hydroxide with a liquid to solid ratio of 3 ml?g-1for 3 h

3.2 Purification of leach liquor

In the leaching process,impurities(Si,As,and P)were also leached along with molybdenum.These impurities can be removed by using magnesium salts because of the low solubility of MgSiO₃,MgHAsO₄,and MgHPO₄[15,16].The purification of leach liquor was performed by adding MgCl₂in the presence of H₂O₂as an oxidant.AsO₃^3-was first oxidized to AsO₄^3-,and then,AsO₄^3-;and PO₄^3-was hydrolyzed to corresponding HAsO₄^2-and HPO₄^2-with the decreasing pH of leach liquor.The reactions for removal of impurities can be described by the following equations:

Under the suitable condition(addition of 1.2 wt%Mg Cl₂,adjusting pH to around 10,and stirring 1 h at 60°C),over97%of impurities(Si,As,and P)could be removed from the leach liquor.The loss rate of molybdenum was less than 1%.The purification result of leach liquor is listed in Table 2.

3.3 Production of calcium molybdate

Leach liquor can be processed by different methods including hydrogen reduction[17],precipitation[18,19],ion exchange[20],carbon adsorption[21],or solvent extraction[22,23]to recover molybdenum as metallic molybdenum,molybdenum trioxide,or ammonium molybdate.Therefore,laboratory experiments were carried out to achieve calcium molybdate product using chemical precipitation method in the present study.

Table 2 Purification result of leach liquor 下载原图

Table 2 Purification result of leach liquor

Table 3 Chemical composition of the CaMoO₄product 下载原图

Table 3 Chemical composition of the CaMoO₄product

Stoichiometric quantities of CaCl₂were added into the purified leach solution to precipitate MoO₄^2-as CaMoO₄under vigorous stirring for overnight.At this stage,calcium molybdate formation took place as per the Reaction(9),and 95.1%of Mo could be precipitated.

The precipitate obtained was dried at 70°C.The chemical composition of CaMoO₄product is listed in Table 3.The whole Mo recovery could reach about 82.7%.The process proposed gives a feasible alternative for the processing of oxygen pressure water leaching residue of Ni–Mo ore,which can be applied in comprehensive utilization of lowgrade molybdenum ores.

4 Conclusion

In alkaline leaching process,more than 88%of molybdenum was leached under the optimum conditions(2.5 mol?L^-1NaOH,80°C,a L/S of 3 ml?g^-1,and reaction time 3 h).Over 97%of impurities(Si,As and P)could be removed from the leach liquor,and the loss rate of molybdenum was less than 1%,respectively.CaMoO₄product with purity of 99.2%could be obtained by CaCl₂precipitation method.The whole Mo recovery reached about 82.7%.

The process proposed gives a feasible alternative for the processing of oxygen pressure water leaching residue of Ni–Mo ore,which can be applied in comprehensive utilization of low-grade molybdenum ores.