硫酸鎂亞型鹽湖鹵水高溫蒸發(fā)析鹽結(jié)晶規(guī)律

謝紹雷1，汪小涵1，景燕1，陳高琪2，紀(jì)律2，張全有1，賈永忠1*

(1.中國(guó)科學(xué)院青海鹽湖研究所，青海 西寧 810008; 2. 茫崖興元鉀肥有限責(zé)任公司，青海 格爾木 816000)

摘要：針對(duì)青海大浪灘鹽湖區(qū)硫酸鎂亞型鹽田鹵水進(jìn)行了高溫蒸發(fā)結(jié)晶規(guī)律的研究，結(jié)果表明該鹽田鹵水在102~122 ℃高溫蒸發(fā)時(shí)析鹽順序?yàn)椋篗gSO4·H2O、NaCl、MgSO4·6H2O、KCl·MgCl2·6H2O和其他混鹽. 通過(guò)對(duì)不同溫度下的液相組分分析和固相X射線衍射分析表明，利用高溫蒸發(fā)開(kāi)采此種鹵水時(shí)，最適宜的蒸發(fā)溫度應(yīng)控制在117 ℃左右. 此時(shí)，該鹵水組成中的質(zhì)量分?jǐn)?shù)低于2%，同時(shí)K+還未析出，可以簡(jiǎn)化為Na+, K+, Mg2+//Cl-—H2O四元體系，以便達(dá)到開(kāi)采氯化鉀的工藝需求，為該鹽湖鹵水的綜合開(kāi)發(fā)利用提供理論參考.

關(guān)鍵詞：鹽湖；硫酸鎂亞型鹵水；高溫蒸發(fā)；結(jié)晶規(guī)律

Received date：2015-04-23.

Foundation item：National Natural Science Foundation of China (21373252) and Youth Guide Foundation of Qinghai Institute of Salt Lakes, Chinese Academy of Sciences.

Biography：XIE Shaolei(1985-), male, research assistant, majoring in the comprehensive utilization of salt lake resources.*Corresponding author, E-mail: jiayzh@hotmail.com.

Dalangtan Salt Lake, located in the northwest of Qaidam Basin which contains abundant salt lake minerals and brine resources, is the second largest salt lake in Qaidam Basin[1]. The intercrystalline brine in Dalangtan Salt Lake, is the typical magnesium sulfate subtypes brine, in which the mass fraction of potassium chloride is 3%-4% and the total quantity of liquid potash is more than 10 million tons. Moreover, solids potash salts resources deposit in 50 m of shallow surface layer, including potassium chloride (5%-10%) and the amounts also up to 10 million tons[2-3].

With the expansion of KCl production scale and excessive consumption of high grade potassium-bearing brine resources, the salt lakes manufacturers, who adopting traditional solution mining-sun curing process to produce carnallite using low-grade potassium brine. How to seek a variety of brine conversion process and exploit the low grade potassium resource have become a focus. Thus the low grade potassium brine resource was studied on the basis of phase diagram theory guidance by many researchers[4-5]. However, there were still many problems existing when exploit the low grade potassium resource, such as longer metallogenic time, high cost and complex operation and so on, which lead to salt lake enterprise much worse. Moreover, the potash production path was seldom reported by researchers[6-7], especially lacking of the data on the evaporating crystallization behavior of the magnesium sulfate subtypes brine at high temperature[8].

In this paper, we reported the potassium process of magnesium sulfate subtypes brine. Taking low grade potassium salt lake brine as the study object, and phase diagram as the guidelines, carnallite was prepared by evaporation and controlled crystallization process using the magnesium sulfate subtypes brine at high temperature, in order to guide the actual production, which further providing some reliable data to exploit the kind of brine.

1Experimental

1.1　Raw Material

The magnesium sulfate subtypes brine was collected from Dalangtan Salt Lakes in summer, belonging to Qinghai Mangai Xingyuan Potash Limited Liability Company. Raw brine ions compositions by chemical titration analysis were shown in Table 1.

Table 1　The ions composition of the raw magnesium

1.2　Experimental devices

The experiment devices of evaporation of the magnesium sulfate subtypes brine at high temperature were shown in Fig.1. To accurately control the temperature of evaporating, the multichannel digital display meter and computer were used in this process.

Fig.1　Schematic diagram of experimental devices of evaporating brine at high temperature

1.3　Analytical method

1.4　Experimental process

We took 1 000 g magnesium sulfate subtypes brine into a 2 L beaker, and put them on above-mentioned experimental devices. After programmed temperature rising, mechanical stirring, computer recording (heating time, speed and boiling temperatures of brine) the brine was slowly heated until solid phases were precipitated. Following, the solid and liquid sample were collected separately by in-situ sampling method at intervals of 0.5 ℃ until the boiling temperature up to 122 ℃.

2Results and discussion

According to the above-mentioned experimental processes and evaporating the magnesium sulfate subtypes brine between 102 ℃ to 122 ℃, we found that the boiling temperatures of salt brine was 103.5 ℃, and the first solid precipitates was separated at 110.3 ℃. The liquid phase and solid phase were rapidly separated by in-situ sampling method and analyzed by X-ray diffraction, respectively. Fig. 2 was the XRD pattern of the solid phase between 111.3 ℃ and 119.3 ℃. We discovered that the solid precipitates sequence was MgSO4·H2O (M1) and NaCl (Ha) mixtures, MgSO4·6H2O (M6) and KCl·MgCl2·6H2O (Car). By our experimental results, the whole evaporation process at high temperature might be divided into four stages: M1and Ha stage mixtures, M6stage and Car stage during evaporating the magnesium sulfate subtypes brine at high temperature. When we continued raising the temperatures, a mass of potassium would precipitated, which was disadvantageous to produce the potassium chloride. So the most suitable evaporating temperature should be controlled at 117 ℃.

Fig.2　X-ray diffraction pattern of solid crystallization at high temperature

The material balance diagram of evaporating and cooling crystallization of the magnesium sul-

Fig.3　Changed points of liquid phase composition in Na +, K +, Mg 2+//Cl -, SO 2- 4—H 2O at 25 ℃

Fig.4　Changed points of liquid phase composition in Na +, K +, Mg 2+//Cl -, SO 2- 4—H 2O at 110 ℃

Fig.5　X-ray diffraction pattern of solid crystallization at 116.3 ℃

Fig.6　The material balance diagram of evaporating salt brine at 117 ℃

fate subtypes brine were detailedly studied. The material balance diagram of evaporating salt brine at 117 ℃ was described in Fig.6. The research results showed that the solid salts from hot filtration weighted 95.07 g and 441.83 g for water when 1 000 g salt brine was evaporated. At the end of the process, 66.12 g of carnallite products was obtained when cooling down to 25 ℃. In other words, about 20 kg of potassium chloride would be produced from a ton of the magnesium sulfate subtypes brine.

3Conclusion

References:

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