Traditional modern salt lake water salt system

Traditional salt lake water salt system research content: the physical properties of brine and chemical properties and water salt system phase equilibrium. Brine physical properties of brine color, turbidity, density, brine layering phenomenon, etc., the chemical properties of brine brine is the main study of brine composition and solarization of the brine chemistry of the salt field. It should be noted that the above research content can not avoid the biological and biological role and its impact on the physical and chemical properties of brine.

I. Physical properties of brine

1. The color of the salt lake water

The color of the water of the salt lake is varied, counting blue-green, slightly red, pink, red, etc. The same salt lake in different seasons, the color of the brine is also the color of the salt lake. The color of the same salt lake is different in different seasons. Ancient people have recorded the color of the salt lake water. More than two thousand years ago, the Northern Wei Dynasty Li Daoyuan in his book "Water Classic Note" wrote: "now the pool of water (Shanxi Yuncheng Salt Lake) seventy miles east and west, seventeen miles north and south, purple Pavilion, muddy and do not flow". Shen Kuo in the Song Dynasty in his book "Dream Stream Pen Talk" said: "solution to the state salt pool ...... halogen color is red, under the Banquan, slang called 'Chi blood' ...... ". Here, "purple", "red", "Chi blood" refers to the color of the salt lake brine in Yuncheng, Shanxi.

Whether it is a salt lake, or salt ponds, we can see, with the gradual increase in salinity, the color of brine gradually deepen, from green and brown and red. About the cause of the brine color, people in the past that the ionic composition of the brine, but until now, people have a clearer understanding that the color of the different salinity in the life of the bacteria and algae of the amount of different species of living organisms. Li Daoyuan said the "purple", Shen Kuo said the "red" and "blood red" show that at that time the brine of the Yuncheng Salt Lake has grown a large number of red halophilic bacteria, halophilic algae and red brine shrimp and other organisms.

2. Turbidity

The turbidity of the brine of the salt lake changes with location and time. Turbidity is determined by algae and suspended salt minerals and non-salt mineral debris. In the case of a sodium sulfate salt lake, for example, the turbidity of the brine decreases rapidly in the spring when mannite dissolves and newly hatched brine shrimp and brine fly larvae consume the algae. Living in the salt lake brine shrimp and brine fly larvae is a natural "cleaner", it makes the brine turbidity less and less.

3. Density

The density of the brine in a salt lake is an inverse effect of the seasonal, annual and long-term changes in lake level.

4. Stratification

The brine in a typical salt lake is divided into two distinct layers: the upper part is more transparent and odorless, and the lower part is denser. For example, the United States in the Great Salt Lake South Bay, to the water depth of 6.08 ~ 6.99m as the boundary, divided into the upper and lower layers, the upper layer of the lake water odorless and transparent, the lower layer of the density of the density of the drastic increase and pollution is heavier. 1979 in the water depth of 3m at the density of 1.089 ~ 1.110g/cm3, 7.6m at the density of 1.166 ~ 1.170g/cm3.

5. Brine temperature

Fluctuations in brine temperature can lead to changes in the degree of ion saturation, which will cause selective precipitation and dissolution of salts in the brine.

The brine temperature is variable, varying with the day, night and season.

(1) average brine temperature

When the brine evaporates, some crystals formed on the surface of the brine, once sunk to the bottom of the pool, due to the change in conditions, it will decompose or dissolve, and the decomposition rate is related to the brine temperature difference and concentration changes and other factors. Experiments show that the actual temperature of the brine in the pool is 0.6 to 0.8 times the air temperature, and in the same pool of brine up and down the concentration is also different, many salt crystals are not in equilibrium with the brine in which they are located. Therefore, the average temperature of the brine is usually the best judge in predicting the type of salt crystallization at the bottom of a sedimentary pool.

(2) Diurnal Temperature Variability Cycles of Brines

Diurnal temperature variations of brines are distinct and regular. Brine day and night temperature changes directly affect the precipitation of salt. For example, the Great Salt Lake in the United States, when the daytime temperature of 35 ℃, in the natural salt field conditions, favorable potassium salt magnesium alum (MgSO4-KCl-3H2O) generation, while at night, when the temperature drops to 15 ℃, it is favorable to the formation of soft potassium magnesium alum (MgSO4-K2SO4-6H2O). Because Ion is sensitive to temperature, etc., so containing Salts can be precipitated at lower temperatures, resulting in a single pool in the same brine can be obtained within the mixture of two salts. Another example, in Xinjiang Barkun Salt Lake, summer mornings can be seen in the night crystallization of long columnar crystals of manganese nitrate, and near noon when the sun provides enough activation energy can make a few hours before the crystallization of manganese nitrate and all dissolved.

(3) Seasonal Temperature Changes

Seasonal temperature changes in salt lakes can affect the deposition of salts. For example, the Great Salt Lake in June to August deposition of salts in the winter cold temperatures and rain, converted to other salts, these salts have the potential to undergo comprehensive chemical changes. For example, the potash magnesium alum can be transformed into hard clumps of potassium chloride and laxative salts, whereas it can be transformed into soft potash magnesium alum if it comes into contact with sulfate-containing brines. In contrast, mannite precipitates in winter and redissolves in summer.

6. Evaporation rate

Evaporation occurs at the surface of the brine, where salt crystallization also takes place. The higher the evaporation rate, the greater the possibility of brine supersaturation and salt formation. When the brine surface salt crystallization density is greater, it will sink to the bottom of the pool (or the bottom of the lake).

Factors affecting the evaporation rate of the sun's baking, the wind blowing, which is the traditional understanding. In recent years, through the brine salinophilic organisms research, the results found that the red salinophilic bacteria algae and red brine shrimp and other organisms can make the whole brine dyed red, and its absorption of sunlight, not only make the brine temperature, but also increase the rate of evaporation.

7. Brine depth and salt crystallization particle size

The depth of the salt field and salt crystallization particle size has a close relationship. For example, in the crystallization pool of the salt field, in the depth <7.6cm and depth >30.5cm, the grain size of the crystallized rock salt is smaller than the grain size of the rock salt crystallized between the depth of 7.6cm and 30.5cm.

Second, the chemical properties of brine

The chemical properties of brine in the salt lake brine is mainly studied in the cation and anion, trace ions, radioactive chemical composition.

Modern salt lake brine according to the composition of the brine (lake surface brine, inter-crystalline brine, silt brine) can be divided into four major categories of chloride type, sulfate type, carbonate type, nitrate type (Zheng Xiyu, 1993). The salts precipitated from different types of salt lake brines are different.

It should be noted that the types of salt lake brine talked about above are not static, but change with the constraints of changing conditions. For example, the evolution of hydrochemical types of salt lakes in Xinjiang is a proof of this. The HCO3-Cl-Ca-Na type of water in the bedrock mountainous areas, with the continuous dissolution and filtration of the elements moving in and adsorption, exchange, oxidation, precipitation, precipitation, precipitation, diffusion, and other chemical, thermodynamic, hydrodynamic and other factors, the transition to the HCO3-SO4-Ca-Mg and SO4-Cl-Na-Mg type of water, and then to SO4-Na-Mg, or even Cl-Na type of water (Zhang Minggang,

Minggang 1993). 1993). The concentration and density of the brine changed from small to large, and the pH changed from weakly acidic to weakly alkaline.

Three, the brine chemistry of solarization salt field

The practice of artificial salt field shows that the chemical reaction in the salt field is affected by the natural conditions such as wind, rain and temperature change. The main factors affecting the crystallization of minerals in salt flats were considered by chemists and geologists in the past to be the rate of evaporation, brine temperature, brine depth, brine seguencing, residence time, and pool permeability. The authors have thoroughly researched and concluded that the most important factor in the crystallization of minerals, whether by artificial salt ponds or natural crystallization, is biological. This will be described in later chapters.

The production process of the solarization salt field is very different from the study of the phase equilibrium of the water-salt system in the laboratory. The following is an example of the brine chemistry of a solarized salt flat, using the production processes of the Yuncheng Salt Lake in Shanxi Province and the Great Salt Lake Salt Flats in the United States.

1. Salt production process of Yuncheng Salt Lake in Shanxi

Yuncheng Salt Lake in Shanxi is the earliest salt lake developed and utilized in China, with a history of development of about 4,000 to 5,000 years. This salt lake has made outstanding contributions to the development of Chinese civilization. Yuncheng Salt Lake is a typical Na2SO4 subtype water, and the composition of the lake water belongs to Na+, Mg2+/Cl-, tetrameric system. The production of rock salt from Na2SO4 subtype water is an innovation of the ancients, which practiced the Na+, Mg2+/Cl-, system mesostable phase diagram.

Yuncheng Salt Lake early production is: sun exposure, natural crystallization, set of workers fishing. The famous geographer of the Northern Wei Dynasty, Li Daoyuan, wrote in the "Notes on the Water Classic": "Purple Chengting, muddy and not flowing, salt in the water, naturally printing into the day to take the night and day again, the end of the undiminished". However, after the Qin, Han, Wei, Jin, North and South Dynasties and Sui Dynasty production practice, the working people painstakingly explore the Kengtai sun salt method, finally in the heyday of our feudal society in the Tang Dynasty, the Kengtai watering sun method. The Tang dynasty salt ponds Ling Qing Gong Shrine Ode and preface "recorded:" stained to the muddy stream, irrigation to a different source, the yin and yang phase steam, clean and pregnant "process method.

The author in the late 1960s in Yuncheng Salt Lake made a survey work. Now the salt lake salt production situation combined with the history of the salt tanning process for a narrative.

There are three kinds of brine for salt production in Yuncheng Salt Lake: one is the "old beach water", i.e., the lighter water of the lake, generally 5-10°Be′; one is the "Hutuo water", which is also the lake water, but with a larger concentration of 15-20°Be′; the third is the well water, i.e., the water from the salt lake. is well water, that is, from the salt lake well pumped out of the salt brine, its composition is mainly NaCl, which is buried underground tens of meters from the surface of a layer of rock salt by the injection of water to dissolve the salt brine.

According to the Qing Dynasty's Jiang Chunfang's "Hedong Salt Law Preparation", the salt-making process was different because the brine used to make salt was different. For example, the process of using well water is:

Biogenesis of Evaporation Rock

The "Luo" here is the pool that stores brine to be evaporated. The "first Luo" is the first evaporation pool, "two Luo" is the second evaporation pool.

Another example, with the "Hutuo water" salt production process is:

Evaporite biogenic theory

Here, the "scapegoat" refers to the bottom of the pool has a nitrate plate of the evaporation pool. What is the nitrate plate? Nitrate plate refers to the salt after the sun after the liquid crystallization of the salt layer composed mainly of white sodium magnesium alum, due to accumulation, thousands of years of accumulation of nitrate plate is up to several meters thick. The bottom of the evaporation pond laid nitrate plate is mainly to remove the salt in the process of crystallization of "porridge paste" sulfate impurities.

Low concentration of "old beach water" is the most complex salt production process, but also as early as 1,400 years ago has perfected the salt production process, which is the Yuncheng Salt Lake, the ancient salt people of the history of salt science and technology of a great contribution. Its salt production process is as follows:

Evaporite biogenic theory

The "circle" here refers to the bottom of the pool without nitrate plate, just mud bottom of the evaporation pool.

Using modern physicochemical language to understand the above production process summarized by the ancients is: low concentration of "old beach water" by the first, second, third circle evaporation pool evaporation, completed the brine evaporation and concentration of the primary stage, to the "ghost" evaporation pool, at which time, the "circle" is the bottom of the pool without nitrate plate, just mud bottom evaporation pool. "Evaporation pool, this time the brine due to the emergence of (Na, Mg) SO4, so the beginning of a porridge paste (concentration of about 24 ~ 25 ° Be′) appeared. This is the difference between seawater salt and Na2SO4 subtype water salt, the latter has a sulfate crystallization stage, how to deal with the brine evaporation process of sulfate, that is, (Na, Mg) SO4 porridge paste is the core of this process. Ancient salt people to deal with "porridge paste" like sulfate material process is this: when in the "scapegoat" evaporation pool appeared over-saturated (i.e., porridge paste), add fresh water, so that the elimination of over-saturation, this time the brine is called "Yangshui", in each pool appropriate side dig a small trench (called side trench), its depth should be greater than the depth of the pool. The side trenches are not connected to the brine in the pools, but are separated by a community bank. The brine in the pond is leached through the nitrate plate at the bottom of the pond (commonly known as the leachate). The essence of leaching is that MgSO4 in the sun water reacts with Na2SO4 in the nitrate plate to form sodium magnesium vanadium (Na2SO4-MgSO4-4H2O), Na2SO4 reacts with the nitrate plate to form anhydrous manganese nitrate (Na2SO4), and calcium sulphate reacts with the nitrate plate to form calcium manganese nitrate (Na2Ca(SO4)2). The author under the microscope to study the composition of the nitrate plate found that the main constituent minerals of the nitrate plate is white sodium magnesium alum, followed by anhydrous manganese nitrate and calcium manganese nitrate, which is consistent with the results of the chemical reaction of the brine in the production of salt; Yang water in the flow of nitrate through the honeycomb pore space, remove sulfate material, flow to the side of the trench, this time the water is called the water, the Yin, Yin water and then self-flowing or pumping mode to the crystallization pool, and finally the production of pure salt.

Summary, with Na +, Mg2 + / Cl -, the system of mesostable phase diagram, can explain the ancients summarized the Shanxi Yuncheng salt lake sodium sulfate subtype of water salt "yin and yang phase steam, clear and wash phase pregnant" principle of the process.

It should be noted that the nitrate plate microscopic studies show that minerals such as sodium magnesium alum are composed of brine shrimp and fossilized brine flies, which suggests that organisms play a significant role in the salt production process.

After the founding of New China, Yuncheng Salt Lake not only makes salt, but also produces yuanming powder, and is the main export base of yuanming powder in China.

2. Great Salt Lake salt production process

Great Salt Lake is the largest salt lake in North America, the composition of the material is shown in Table 1-1.

Table 1-1 Great Salt Lake north of the North Bay brine chemical composition

(According to F.J. Post, 1975)

Great Salt Lake salt basking in the single pool and a number of pools connected to pools in series group.

Single-pool salt tanning: the brine of the salt lake is used as raw material, the Mg content is kept at 7%, and rock salt, carnallite, and magnesium hydrochlorite are crystallized.

4 pools of tandem salt: generate lagoon salt, soft potassium magnesium alum, potassium magnesium alum and potassium magnesium alum.

In the solar pond, some salts take longer to crystallize than others, and if they are transferred to another brine pond with a different concentration before they crystallize in the brine, the brine will deposit a different group of salts. For example, by transferring a supersaturated brine which will crystallize the potassium salt magnesium alum, the laxative salt, and the rock salt, to another pool, the resulting mixed brine favors the crystallization of carnallite, while the potassium salt magnesium alum will disappear. The above can be expressed in two chemical reaction equations:

Reaction equation 1:

Evaporite biogenesis

Reaction equation 2:

Evaporite biogenesis