Economically and Environmentally Sustainable Enhanced Oil Recovery. M. R. Islam

of the ammonium-bearing minerals. It forms in natural fumaroles, where gas vents from underground from volcanic activity. It also forms from the process of the burning of coal in coal deposits. The formation of Sal ammoniac is unique, as it is created from sublimation, meaning it crystallizes directly from gaseous fumes and bypasses a liquid phase. Sal ammoniac is highly soluble in water. It is known for its utility in many applications, ranging from fertilizer, to colouring agent to medical usage.

      Sal ammoniac (naturally occurring Ammonium Chloride) has reported to be first found in the wastelands of Central Asia, from which it was used by Muslim Alchemists of the medieval age, primarily for distillation of organic materials (Multhauf, 1965). In later centuries, there is evidence that Sal ammoniac was being produced through solar distillation of camel urine and other organic products, in proportion of five parts urine, one part common salt, and one-half part soot, which was also derived from natural products (Malthauf, 1965). Soot in general is a common source of heavy metals. Whenever soot is formed, they contain heavy metals that act as the nucleation site within the powdery soot. It is also reported that soot collected from the chimney of camel dung furnaces in Egypt contained natural ammonium chloride. This is expected as any herbivorous animal would have natural supply of salt in its diet. The concept of combining ammonia (then known as volatile alkali) and hydrochloric acid (then known as ‘spirit of salt’) wasn’t invented until late 18^th century (Malthauf, 1965). The now well-known synthesis process was:

      (2.1)

      This synthesis process was deemed to be cheaper than the ‘decomposition, which used decomposition of soot (including organic material), sulfuric acid and salt. By the mid-nineteenth century the synthetic process had superseded all others for the manufacture of sal ammoniac, and it was accomplished with utter simplicity through the addition of hydrochloric acid to the “ammonia liquor”, which was a residue from coal distillation.

Later on, another process evolved. It involved double decomposition of ammonium sulfate and sodium chloride:

 (2.2)

      (2.3)

Ammonium carbonate refers to smelling salts, also known as ammonia inhalants, spirit of hartshorn or sal volatile. Today, this chemical is known as baker’s ammonia – the source of gaseous ammonia. It is also the form taken by ammonia when distilled from carbonaceous material without drying. Similarly, copper sulfate can be derived from naturally occurring blue vitriol, other sulfates, such as calcium sulfate (gypsum in its natural state). In Equation 2.2, the requirement is that an insoluble carbonate be formed, permitting the separation of the ammonium sulfate. The separation of the sal ammoniac in the second reaction was accomplished either by its sublimation or by differential crystallization.

      Even later, came the double decomposition of ammonium carbonate and magnesium chloride (bittern), following the reaction:

      (2.4)

      This involved one step less than the preceding process and moreover utilized as a source of magnesium chloride the waste mother liquor, “bittern,” which is the waste of brine after production of common salt and is rich in magnesium chlorides, sulfates, bromides, iodides, and other chemicals present in the original sea water. This process was introduced commercially by the well-known hydrometer inventor, Antoine Baume, only a year after the establishment of the Gravenhorst factory, and we have a circumstantial account of his works written in 1776, while it was still in operation.

      2.2.3 Sulphur

      As per New Science, sulfur is the tenth most abundant element in the universe, has been known since ancient times. Table 2.4 Shows abundance numbers for various elements in the universal scale. On earth, this scenario changes. Table 2.4 lists the most abundant elements found within the earth’s crust.

      Table 2.4 Abundance number for various elements present in the universe (from Heiserman, 1992 and Croswell, 1996).

Element	Atomic number	Mass fraction, ppm	Abundance (relative to silicon)
Hydrogen	1	739,000	40,000
Helium	2	240,000	3,100
Oxygen	8	10,400	22
Neon	10	4,600	8.6
Nitrogen	7	960	6.6
Carbon	6	1,090	3.5
Silicon	14	650	1
Magnesium	12	580	0.91
Iron	26	10,900	0.6
Sulfur	16	440	0.38

      Wexler (2014) points out that the use of sulphur has been popular since the ancient Greek period in production of chemical ‘weapon’. As early as 420 BC, toxic aerosol was created with natural pitch and sulphur powder. This tradition was continued by the Roman, who often added other natural chemicals to increase the deadly effect of the toxic cloud. Similarly, Both ancient Chinese and Indian cultures used sulphur for warfare. They, however, added combustible chemicals, such as explosive saltpeter or nitrate salts, and/or a variety of plant, animal, or mineral poisons, such as arsenic and lead, in making smoke and fire bombs. In even the new world and in India, the seeds of toxic plants and hot peppers have been in use to rout attackers (Wexler, 2014).

      When it comes to using sulphur for material processing or medicinal needs, Muslim scientists of the medieval era are the pioneers (Islam et al., 2010). As pointed out by Norris (2006), the Sulfur–Mercury theory of metal composition by these scientists is paramount to understanding sustainable material processing. This theory is in the core of the so-called exhalation theory that includes continuous transition between solid and gaseous phases. Norris (2006) identified the main strengths of the mineral exhalation theory as compositional flexibility and upward mobility: the mixing of protometallic vapours, which could vary compositionally and react with other mineral matter during their movement through subterranean regions, seemed sufficient for producing a plurality of metals and ores. The Muslim scientists considered metals