Difference between magnesium sulfate monohydrate

The most obvious difference between magnesium sulfate monohydrate and magnesium sulfate heptahydrate is the appearance. Magnesium monohydrate is a white powder solid, while magnesium heptahydrate is a colorless and transparent crystal.


In terms of chemical structure, magnesium monohydrate is a hydrated magnesium sulfate containing one crystal water, with a relative molecular weight of 138, seven crystal water containing seven magnesium heptahydrate and a relative molecular weight of 246. Therefore, magnesium monohydrate and magnesium heptahydrate of the same quality, in which the percentage of magnesium element is 1.78 times of magnesium heptahydrate (therefore, in the agricultural production process, the effective magnesium component of magnesium monohydrate is higher than that of magnesium heptahydrate).


In large-scale industrial production, the raw materials of both are sulfuric acid and magnesium oxide. But the products produced by the same process are also good and bad. This is because some unscrupulous manufacturers choose cheap industrial waste acid as raw material to produce magnesium heptahydrate, in order to reduce the production cost, but there is a great potential safety hazard in this approach, which needs to be analyzed from the source of industrial waste acid.


The main sources of industrial waste acid are metallurgy and electroplating. A lot of acid will be used in metal surface treatment. When the metal samples and other impurities in the acid solution reach a certain concentration and the treatment effect cannot meet the process requirements, the acid solution needs to be reconstituted and replaced. In this process, a lot of waste acid liquid will be produced. These waste acids contain high concentration of acid, cobalt, titanium, chromium, arsenic and other heavy metal elements and a variety of inorganic impurities. Once such industrial waste acid goes into the next production process without treatment, its products will be polluted and even poisoned.


Once such magnesium heptahydrate product is used in agricultural production, it will have a bad impact on the soil it spreads. The acid radical ions and toxic heavy metals carried by the impurity acids in the industrial waste acid will be enriched in the soil, animals and plants, and finally absorbed by the human body.


Compared with magnesium heptahydrate, the situation of using waste acid as raw material for magnesium monohydrate is more optimistic. Due to the characteristics of magnesium monohydrate itself, if waste acid is used as raw material, the magnesium monohydrate product will be gray black instead of normal milky white. The color difference directly determines the product phase. Therefore, most magnesium monohydrate manufacturers prefer high-quality industrial sulfuric acid (concentration 94% - 98%) rather than industrial waste acid.