Draft:Original research/Geochemistry to produce Widgiemoolthalite

"Widgiemoolthalite is a rare hydrated nickel(II) carbonate mineral with the chemical formula (Ni,Mg)5(CO3)4(OH)2·5H2O. Usually bluish-green in color, it is a brittle mineral formed during the weathering of nickel sulfide. Present on gaspéite surfaces".

One consequence of the 1966 discovery of nickel deposits in Western Australia and subsequent nickel mining boom was the discovery of novel secondary mineral species in mined regions starting in the mid-1970s.

"Widgiemoolthalite was first found at 132 North, a nickel deposit near Widgiemooltha, Western Australia, controlled by the Western Mining Corporation. Blair J. Gartrell collected the holotype widgiemoolthalite specimen from a stockpile of secondary minerals at the site."

"The mineral was discovered in 1992 and was first reported in American Mineralogist in 1993 by Ernest H. Nickel, Bruce W. Robinson, and William G. Mumme, when it received its name for its type locality. Widgiemoolthalite's existence was confirmed and name was approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association the same year."

The holotype specimen was stored in Perth's Western Australian Museum (specimen M.1.1993).

"Widgiemoolthalite occurs as a secondary mineral."

It is found overlaying nickel sulfide that has undergone weathering, often in hollow spaces on gaspéite surfaces [...], and often exhibiting fibrous and rarely massive crystal habits. Other minerals associated with widgiemoolthalite include annabergite, carrboydite, dolomite, glaukosphaerite, hydrohonessite, kambaldaite, magnesite, nepouite, nullaginite, olivenite, otwayite, paratacamite, pecoraite, reevesite, retgersite, and takovite. Two additional unnamed minerals were also reported as associated secondary minerals from the 132 North site, the only locality at which widgiemoolthalite had been found as of 2016. The 132 North waste pile from which widgiemoolthalite was first recovered is no longer in existence, making it a rare mineral. In support of the designation of an Anthropocene epoch, the existence and provenance of widgiemoolthalite, along with 207 other mineral species, were cited in 2017 by Robert M. Hazen et al. as evidence of uniquely human action upon global stratigraphy.

Supergene processes
Def. "leached and then deposited by descending waters" is called a supergene process.

"In ore deposit geology sugergene processes or enrichment occurs relatively near the surface. Supergene processes include the predominance of meteoric water circulation with concomittant oxidation and chemical weathering. The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Supergene enrichment occurs at the base of the oxidized portion of an ore deposit at which point the metals are redeposited on hypogene sulfides creating a zone of increased ore content."

This is particularly noted in copper ore deposits where the copper sulfide minerals chalcocite Cu2S, covellite CuS, digenite Cu1.8S, and djurleite Cu31S16 are deposited by the descending surface waters.

All such processes take place at essentially atmospheric conditions, 25 °C and atmospheric pressure.

From the surface down they are different zones: a gossan cap, a leached zone, an oxidized zone, the water table, an enriched zone (supergene enriched zone) and the primary zone (hypogene zone).

Gossan cap
Pyrite FeS2 is generally abundant, and near the surface it oxidises to insoluble compounds such as goethite FeO(OH) and limonite, forming a porous covering to the oxidized zone known as gossan or iron hat.

Leached zone
The groundwater contains dissolved oxygen and carbon dioxide, and as it travels downwards it leaches out the minerals in the rocks to form sulfuric acid, and other solutions that continue moving downwards.

Oxidized zone
Above the water table the environment is oxidizing, and below it is reducing. Solutions traveling downward from the leached zone react with other primary minerals in the oxidised zone to form secondary minerals such as sulfates and carbonates, and limonite, which is a characteristic product in all oxidised zones.

In the formation of secondary carbonates, primary sulfide minerals generally are first converted to sulfates, which in turn react with primary carbonates such as calcite CaCO3, dolomite CaMg(CO3)2 or aragonite (also CaCO3, polymorphic with calcite) to produce secondary carbonates. Soluble salts continue on down, but insoluble salts are left behind in the oxidised zone where they form. An example is the lead mineral anglesite PbSO4. Copper may be precipitated as malachite Cu2(CO3)(OH)2 or azurite Cu3(CO3)2(OH)2. Malachite, azurite, cuprite Cu2O, pyromorphite Pb5(PO4)3Cl and smithsonite ZnCO3 are stable in oxidising conditions and they are characteristic of the oxidation zone.

Water table
At the water table the environment changes from an oxidizing environment to a reducing one.

Enriched zone
Copper ions that move down into this reducing environment form a zone of supergene sulfide enrichment. Covellite CuS, chalcocite Cu2S and native copper Cu are stable in these conditions and they are characteristic of the enriched zone.

The net effect of these supergene processes is to move metal ions from the leached zone to the enriched zone, increasing the concentration there to levels higher than in the unmodified primary zone, possibly producing a deposit worth mining.

Primary zone
The primary zone contains unaltered primary minerals.

Nickel sulfides
Nickel(II) sulfide is insoluble in water.

Millerites
Millerite is a nickel sulfide mineral, NiS. Millerite is a common metamorphic mineral replacing pentlandite within serpentinite ultramafics. It is formed in this way by removal of sulfur from pentlandite or other nickeliferous sulfide minerals during metamorphism or metasomatism.

Millerite is also formed from sulfur poor olivine cumulates by nucleation. Millerite is thought to form from sulfur and nickel which exist in pristine olivine in trace amounts, and which are driven out of the olivine during metamorphic processes. Magmatic olivine generally has up to ~4000 ppm Ni and up to 2500 ppm S within the crystal lattice, as contaminants and substituting for other transition metals with similar ionic radii (Fe2+ and Mn2+).

During metamorphism, sulfur and nickel within the olivine lattice are reconstituted into metamorphic sulfide minerals, chiefly millerite, during serpentinization and talc carbonate alteration. When metamorphic olivine is produced, the propensity for this mineral to resorb sulfur, and for the sulfur to be removed via the concomitant loss of volatiles from the serpentinite, tends to lower sulfur fugacity.

This forms disseminated needle like millerite crystals dispersed throughout the rock mass. Millerite may be associated with heazlewoodite and is considered a transitional stage in the metamorphic production of heazlewoodite via the above process.

"Millerite, NiS, fractured under high vacuum and reacted with air and water has been analyzed by X-ray photoelectron spectroscopy (XPS). The pristine millerite surface gives rise to photoelectron peaks at binding energies of 853.1 eV (Ni 2p3/2) and 161.7 eV (S 2p), thus resolving ambiguities concerning binding energies quoted in the literature. Air-reacted samples show the presence of NiSO4 and Ni(OH)2 species. There is evidence for polysulfide species ($$S^{2-}_n$$􏰄, where 2 􏰀≤ n 􏰀≤ 8) on air-oxidized surfaces. These may occur in a sub-surface layer or may be intermixed with the Ni(OH)2 in the oxidized layer. The NiSO4 species at the millerite surface occur as discrete crystallites whereas the Ni(OH)2 forms a thin veneer covering the entire millerite surface. The NiSO4 crystallites form on the surface of millerite but not on surfaces of adjacent minerals. Surface diffusion of Ni2+􏰃 and $$SO^{2-}_4$$ across the millerite surface [may] be responsible for the transport and subsequent growth of NiSO4 crystallites developed on millerite surfaces. [It] is clear that Ni and $$SO^{2-}_4$$􏰄 does not diffuse onto surfaces of adjacent minerals in sufficient quantity to form crystallites [...]. XPS results for water-reacted surfaces show little difference from the vacuum fractured surfaces with the exception that minor amounts of polysulfide and hydroxy nickel species are present. Similar reaction products to those formed in air [NiSO4 and Ni(OH)2] are believed to be produced, but these are removed from the millerite surface by dissolution, leaving behind a sulfur-enriched surface (polysulfide) and hydroxyl groups chemisorbed to nickel ions at the millerite surface."

"The presence of NiSO4 can be explained through oxidation of the sulfide ion in millerite to sulfate by molecular oxygen according to the following scheme:
 * NiS +􏰃 2O2 → NiSO4

In fact, it is most likely that the salt is hydrated. The presence of water in the O 1s spectrum supports the suggestion. The free energy of formation of hydrated NiSO4 species is about 300 to 400 kcal/mol more negative than anhydrous NiSO4, the difference being largest for the greatest degree of hydration. Even without hydration, the oxidation of NiS to NiSO4 by molecular oxygen has a [reaction (rxn)] 􏰉∆Grxn 􏰅= -􏰄162.6 kcal/mol. Therefore, the oxidation of NiS to NiSO4 is thermodynamically favored and should occur provided it is kinetically favored."

"Coincident with formation of the hydroxy nickel surface complex is the formation of polysulfides. The nickel that reacts with the water and oxygen of ambient air is no longer bonded to sulfide. This sulfide is therefore available to react with other near-surface species, including other sulfide ions, which may lead to the formation of polysulfides (including disulfide) according to the following reaction scheme:"
 * nNiS 􏰃+ (n-􏰄1)H2O 􏰃+ (n-􏰄1)/2O2 → Ni2􏰃􏰄+ - $$S^{2+}_n$$ +􏰃 (n􏰄-1)Ni(OH)2,

"where 2 ≤􏰀 n ≤􏰀 8. The designation Ni2􏰃􏰄+ - $$S^{2+}_n$$ is used to denote polysulfide bonded to nickel in the lattice at the millerite surface. The Ni(OH)2 and polysulfide may exist as separate, thin layers on the millerite surface with the Ni(OH)2 presumably forming the overlayer. Alternatively, the polysulfides may be intermixed with the Ni(OH)2 in the oxidized overlayer."

Heazlewoodites
Heazlewoodite, Ni3S2, is a rare sulfur-poor nickel sulfide mineral found in serpentinitized dunite. It occurs as disseminations and masses of opaque, metallic light bronze to brassy yellow grains which crystallize in the trigonal crystal system. It has a hardness of 4, a specific gravity of 5.82. Heazlewoodite was first described in 1896 from Heazlewood, Tasmania, Australia.

Heazlewoodite is formed within terrestrial rocks by metamorphism of peridotite and dunite via a process of nucleation. Heazlewoodite is the least sulfur saturated of nickel sulfide minerals and is only formed via metamorphic exsolution of sulfur from the lattice of metamorphic olivine.

Heazlewoodite forms from sulfur and nickel which exist in pristine olivine in trace amounts, and which are driven out of the olivine during metamorphic processes. Magmatic olivine generally has up to ~4000 ppm Ni and up to 2500 ppm S within the crystal lattice, as contaminants and substituting for other transition metals with similar ionic radii (Fe2+ and Mg2+).

During metamorphism, sulfur and nickel within the olivine lattice are reconstituted into metamorphic sulfide minerals, chiefly millerite, during serpentinization and talc carbonate alteration.

When metamorphic olivine is produced, the propensity for this mineral to resorb sulfur, and for the sulfur to be removed via the concomitant loss of volatiles from the serpentinite, tends to lower sulfur fugacity.

In this environment, nickel sulfide mineralogy converts to the lowest-sulfur state available, which is heazlewoodite.

Heazlewoodite is known from few ultramafic intrusions within terrestrial rocks. The Honeymoon Well ultramafic intrusive, Western Australia is known to contain heazlewoodite-millerite sulfide assemblages within serpentinized olivine adcumulate dunite, formed from the metamorphic process.

The mineral is also reported, again in association with millerite, from the ultramafic rocks of New Caledonia.

Violarites
Violarite (Fe2+Ni23+S4) is a supergene sulfide mineral associated with the weathering and oxidation of primary pentlandite nickel sulfide ore minerals.

Violarite is formed by oxidisation of primary sulfide assemblages in nickel sulfide mineralisation. The process of formation involves oxidation of Ni2+ and Fe2+ which is contained within the primary pentlandite-pyrrhotite-pyrite assemblage.

Violarite is produced at the expense of both pentlandite and pyrrhotite, via the following basic reaction;

Pentlandite + Pyrrhotite --> Violarite + Acid
 * (Fe,Ni)9S8 + Fe(1-x)S + O2 → Fe2+Ni23+S4 + H2SO3

Violarite is also reported to be produced in low-temperature metamorphism of primary sulfides, though this is an unusual paragenetic indicator for the mineral.

Continued oxidation of violarite leads to replacement by goethite and formation of a gossanous boxwork, with nickel tending to remain as impurities within the goethite or haematite, or rarely as carbonate minerals.

Violarite is reported widely from the oxidised regolith above primary nickel sulfide ore systems worldwide. It is of particular note from the Mount Keith dunite body, Western Australia, where it forms an important ore mineral.

It is also reported from open cast mines around the Kambalda Dome, and Widgiemooltha Dome, in association with polydymite, gaspeite, widgiemoolthalite and hellyerite, among other supergene nickel minerals.

Retgersites
Aqueous solutions of nickel sulfate react with sodium carbonate to precipitate nickel carbonate, a precursor to nickel-based catalysts and pigments. Addition of ammonium sulfate to concentrated aqueous solutions of nickel sulfate precipitates Ni(NH4)2(SO4)2·6H2O, a blue-coloured solid analogous to Mohr's salt, Fe(NH4)2(SO4)2·6H2O.

Nickel sulfate occurs as the rare mineral retgersite, which is a hexahydrate. The second hexahydrate is known as nickel hexahydrite (Ni,Mg,Fe)SO4·6H2O. The heptahydrate, which is relatively unstable in air, occurs as morenosite. The monohydrate occurs as very rare mineral dwornikite (Ni,Fe)SO4·H2O.

Népouites
Népouite is a rare nickel silicate mineral which has the apple green colour typical of such compounds. The ideal formula is Ni3(Si2O5)(OH)4, but most specimens contain some magnesium, and (Ni,Mg)3(Si2O5)(OH)4 is more realistic. There is a similar mineral called lizardite (named after the Lizard Complex in Cornwall, England) in which all of the nickel is replaced by magnesium, formula Mg3(Si2O5)(OH)4. These two minerals form a series; intermediate compositions are possible, with varying proportions of nickel to magnesium.

Garnierites
Garnierite is a general name for a green nickel ore which is found in pockets and veins within weathered and serpentinized ultramafic rocks. It forms by lateritic weathering of ultramafic rocks and occurs in many nickel laterite deposits in the world. It is an important nickel ore, having a large weight percent NiO.

Some of the proposed compositions are all hydrous Ni-Mg silicates, a general name for the Ni-Mg hydrosilicates which usually occur as an intimate mixture and commonly includes two or more of the following minerals: serpentine, talc, sepiolite, smectite, or chlorite, and Ni-Mg silicates, with or without alumina, that have x-ray diffraction patterns typical of serpentine, talc, sepiolite, chlorite, vermiculite or some mixture of them all.

The composition of a talc-like garnierite is close to the compositions of stevensite and sepiolite, but with partial replacement of the Mg content by Ni. Chemical analysis of garnierite samples yields non-stoichiometric formulae that can be reduced to formulas like those of talc and serpentine suggesting a talc monohydrate formula of H2O(Mg,Ni)3Si4O10(OH)2 for the talc-like garnierite. Mg, Si, Fe, Ni and Al have been found in samples and the compositions of all these garnierite samples lie between the serpentine solid solution series and the sepiolite solid solution series. Using x-ray diffraction, the composition of garnierite samples collected at the Falcondo mine in the Dominican Republic fell into one of three groups: an Ni-talc to willemseite (up to 25 weight percent Ni) group, an Ni-lizardite to nepouite (up to 34 weight percent Ni) group and an Ni-sepiolite to falcondoite (up to 24 weight percent Ni) group. Using Extended X-ray Absorption Fine Structure (EXAFS) analysis to determine the composition of their garnierite samples, they had an almost complete solid solution between Ni-sepiolite and falcondoite, with samples analyzed showing between 3 and 77 percent falcondoite composition. According to X-ray and thermal analysis, the garnierites of the Ural deposits are multiphase formations and consist of a serpentinites (pecoraite 2McI, chrysotile 2McI, chrysotile 2OrcI, lisardite 6T, lisardite 1T, nepuit - nickel lisardite 1T), chlorites (clinochlor IIB, sepiolit, palygorskit), clay minerals (nontronit, saponite, montmorillonite, vermiculite), minerals of the mica supergroup (talc, vilemsite, clintonite, annite, phlogopite) and quartz. Calcite, sauconite, beidellite, halloysite, thomsonite, goethite, maghemite, opal, moganite, nickel hexahydrite, accessory magnesiochromite and rivsit are among the sporadic minerals found in them.

The unit cell parameters, found using transmission electron microscopy (TEM) analysis, are 13.385(4), 26.955(9), 5.271(3) Å and 13.33(1), 27.03(2), 5.250(4) Å, space group Pncn.

Based on the ionic radii and charge alone, Ni2+ should easily substitute for Mg2+ in octahedral coordination. The fact that Ni readily substitutes for Mg in garnierite explains why as NiO content goes up, MgO content goes down. The nickel in garnierite is not evenly distributed throughout the structure, but is concentrated in small zones of nickel surrounded by magnesium zones. Garnierite is a layer silicate. The main difference between the serpentine-like and talc-like variants of garnierite is the spacing between layers in the structure, seen in x-ray powder diffraction studies. The serpentine-like variants have 7 Å basal spacings while the talc-like variants have a basal spacing of 10 Å. At 106X magnifications, the 7 and 10 Å layer spacings (d(001)) are obvious and measureable, with the 7 Å spacings being better defined than the 10 Å spacings. 7 Å, serpentine-like minerals show rod and tube shaped particles, as well as platy particles and fluffy particles that are most likely aggregates while the 10 Å variety shows much less variation in particles, showing only platy and fluffy forms with very few tube or rod shaped particles. Some particles exhibit interstratification of 7 and 10 Å spacings. There is no correlation between NiO content and the shapes of the particles in the mineral. 7 Å type garnierites usually resemble chrysotile or lizardite in their structures, while 10 Å types usually resemble pimelite.

Garnierite is a green mineral, ranging from light yellow-green to dark green. The color comes from the presence of nickel in the mineral structure for magnesium. Noumeaite (later determined to be a member of the garnierite family) varies in hardness, from soft and brittle to hard enough to carve into figurines and the like. Some species of garnierite stick to the tongue and dissolve readily in water or even on the tongue. Garnierite commonly has a colloform texture, typical of minerals that fill open spaces from a solution. In general, darker green garnierites have higher Ni content, higher specific gravity and higher mean index of refraction than lighter green garnierites, which most likely relates to the inclusion of more Ni in the structure. The Specific gravity of garnierite ranges from approximately 2.5 to 3. The mean index of refraction of garnierite ranges from approximately 1.563 to 1.601.

Light colored garnierite is an alteration of olivine-rich rock to a clay-like mineral poor in nickel, light green to bright green garnierite is a result of the leaching of manganese oxide, magnesium, nickel and iron from the original dark green garnierite, rich in nickel, which was deposited by groundwater. This leads to a very common occurrence of garnierite as fracture fillings of millimeter to centimeter thick veins or as a fabric or coatings at the Falcondo mine in the Dominican Republic. X-ray diffraction of samples from that mine show that garnierite veins include sepiolite-falcondoite and quartz (chrysoprase, a green variety of quartz with a nickel content of less than 2 weight %). Breccias found in faults at the Falcondo mine contain garnierite clasts cemented together by a secondary deposition of garnierite, which is evidence of syn-tectonic deposition of garnierite. In the garnierite deposits near Riddle, Oregon, garnierite is found as a weathering product of the underlying peridotite, with the garnierite layer between 50 and 200 ft thick.

Carbonates
"In nature there exists two hydroxy nickel carbonate minerals nullaginite Ni2(CO3)(OH)21-3 and zaratite Ni3(CO3)(OH)4⋅4(H2O)4-8. Other non-mixed cationic nickel carbonates include hellyerite NiCO3⋅6H2O9, widgiemoolthalite Ni5(CO3)4(OH)2⋅5H2O10 and otwayite Ni2CO3(OH)2⋅H2O11. There are a significant number of nickel carbonates with mixed cations especially with a layered double hydroxide structure which include carboydite, comblainite, mountkeithite, reevesite and takovite12-18. Nullaginite is monoclinic with point group 2/m and is a member of the rosasite mineral group. Nullaginite is formed in the oxidised zone of nickel rich hydrothermal ore deposits. Zaratite is of an unknown structure and is an uncommon secondary mineral formed by alteration of chromite, pentlandite, pyrrhotite and millerite in ultramafic rocks."

"The gaspeite-hellyerite-nullaginite assemblage and the relative stability of the minerals [...] are the stable minerals at one atmosphere. Such minerals may be used as a sink for carbon dioxide."

Pumping "liquid CO2 below the ground where suitable nickel deposits are found could result in the formation of nullaginite and zaratite [...]."

"The mineral aurichalcite (Zn,Cu2+)5(CO3)2(OH)6 is also monoclinic as are many of the other hydroxy carbonates such as malachite39-41." As is widgiemoolthalite.

Hydroxides
"Periclase is a rare magnesium oxide mineral. It is usually found as a component of metamorphosed dolomitic limestones. May be associated with pyrometamorphism (e.g., coal fires). It can hydrate and alter to Brucite and other magnesium minerals by action of the humidity in normal atmospheric conditions."

"Although MgO exhibits numerous advantages, such as a high melting point of 2825°C, basic slag and corrosion resistance, it is susceptible to react with water. This reaction results in the formation of brucite Mg(OH)2 according to Equation 1 [1-3]":
 * $$MgO + H_2O$$(liquid or water vapor)$$ = Mg(OH)_2$$ (1)

"The hydration reaction of periclase can take place during long transport of magnesia from remote countries. It may also occur during storage of the material as well as mixing with water or curing of the castable mixture [3- 7]. Time and high humidity promote the MgO hydration reaction greatly which results in a large volumetric expansion due to the fact that the density of formed brucite Mg(OH)2 is by 33 % lower than the density of periclase MgO. The increase of volume leads to the tensile and compressing stresses formation what results in cracks and subsequent damage of the material [3, 4, 6, 8, 9, 10, 12]."

"According to the literature [9, 11] there are a few factors that influence magnesia hydration reaction. These are chemical and phase composition of magnesia raw materials, size and crystallographic orientation of the MgO crystals, temperature of environment as well as relative humidity and time. The higher temperature, time and pressure of water vapour, the higher the hydration rate. Moreover, the smaller crystal sizes, higher specific surface area and pore volume of the oxide particles, the easier and faster hydration reaction."

The "mechanism of the MgO hydration reaction with water vapour [is] a multistep process which proceeds stepwise [13, 1]:

a) physical adsorption of water vapour on the surface of MgO crystal and formation of a layer of liquid water,

b) chemical reaction between water molecules and MgO resulting in a formation of a thin layer of Mg(OH)2,

c) Mg(OH)2 dissolution in the water layer,

d) supersaturation of the water layer with Mg2+ and OH- ions and subsequent crystallization of Mg(OH)2."

The "mechanism of MgO hydration with liquid water consists of three primary steps, [14], which are as follows:

a) adsorption of water on the surface of MgO and its simultaneous diffusion through the pores inside the MgO grains,

b) dissolution of MgO by the absorbed water and a related change of porosity,

c) supersaturation of water with Mg2+ and OH- ions leading to nucleation and growth of Mg(OH)2 on the MgO crystals surface."

At or below the water table
"Suitable nickel salts are those reducible by zinc and other reducing metals such as magnesium. These compounds include nickel halides, nickel sulfates, nickel phosphates, nickel carbonates, nickel salts of organic acids, such as nickel formate, nickel acetate, and the like."

"Lime neutralization is widely used to precipitate heavy metals including copper and nickel from waste-water. Limestone (calcium carbonate: CaCO3) is too stable to be used directly for this purpose. Grinding of CaCO3 in the solutions of copper and nickel sulfate was conducted to raise its reactivity. During the mechanochemical activation, CaCO3 reacted with copper sulfate to form insoluble copper compounds as basic carbonate and basic sulfate. No reaction between CaCO3 and nickel sulfate occurred even with such activation."

"Since the solubility product of Cu(II) sulfide is much lower than that of Ni(II) sulfide, Cu(II) will be separated from the Ni(II) solution by adding moderate amount of sulfide into the Ni(II) and Cu(II) solutions [18]."

"The most widely used chemical precipitation technique is hydroxide precipitation due to its high removal rate, low cost, a well-developed technique and a simple and convenient operation [22]. Lime milk (Ca(OH)2) neutralization is a widely practiced technique in the hydroxide precipitation [23,24], and the addition of coagulants such as alum, iron salts, and organic polymers can enhance the efficiency of treatment [25]. However, the process of hydroxide precipitation can only achieve the purpose of removing heavy metal ions from water, but not the mutual separation between heavy metal ions in an aqueous solution."

"CaCO3 is stable, easily available, low-cost and insoluble in water, commonly used as an adsorbent for heavy metals [26,27]. However, it is not active as Ca(OH)2 to neutralize the salts to precipitate heavy metals. On the other hand, there exists clear difference in the solubility product constants of CuCO3, NiCO3 and CaCO3 with values of 1.4 x 10-10, 1.42 x 10-7 and 2.8 x 10-9, respectively, at normal temperature and pressure [28]. Such difference may imply a difference between the reactivity of copper and nickel sulfates toward CaCO3 to form the corresponding metal carbonates, if the reactivity of CaCO3 is changed and raised by some reasonable methods."

"Dry grinding is commonly used to trigger the activation effect and direct reaction as well. Grinding solids in the presence of liquids (liquid assisted grinding, LAG) was often reported in organic reactions, in which covalent bonds were suggested to occur principally, or even exclusively, through bulk liquid eutectic states [37]."

"In the present work, the concept of LAG was used to increase the reactivity of CaCO3. As the reactivity of CaCO3 increased up to a level, Cu will be preferentially precipitated by reacting with CaCO3 to form copper carbonate with lower solubility while Ni still exists in aqueous solution. After this reaction, Cu is separated from the Ni solution by solid-liquid separation."

Carbonate–silicate cycles
The carbonate-silicate cycle is the primary control on carbon dioxide levels over long timescales. It can be seen as a branch of the carbon cycle, which also includes the terrestrial biological carbon cycle, or organic carbon cycle, in which biological processes convert carbon dioxide and water into organic matter and oxygen via photosynthesis.

The inorganic cycle begins with the production of carbonic acid (H2CO3) from rainwater and gaseous carbon dioxide. Carbonic acid is a weak acid, but over long timescales, it can dissolve silicate rocks (as well as carbonate rocks). Most of the Earth's crust (and mantle) is composed of silicates. These substances break down into dissolved ions as a result. For example, calcium silicate CaSiO3, or wollastonite, reacts with carbon dioxide and water to yield a calcium ion, Ca2+, a bicarbonate ion, HCO3-, and dissolved silica. This reaction structure is representative of general silicate weathering of calcium silicate minerals. The chemical pathway is as follows:

River runoff carries these products to the ocean, where marine calcifying organisms use Ca2+ and HCO3- to build their shells and skeletons, a process called carbonate precipitation:

Two molecules of CO2 are required for silicate rock weathering; marine calcification releases one molecule back to the atmosphere. The calcium carbonate (CaCO3) contained in shells and skeletons sinks after the marine organism dies and is deposited on the ocean floor.

Washing Soda Method
In this method, water is treated with a calculated amount of washing soda (Na2CO3) which converts the chlorides and sulphates of calcium and magnesium into their respective carbonates which get precipitated:

CaCl2 + Na2CO3 --> CaCO3 + 2NaCl, MgSO4 + Na2CO3 --> MgCO3 + Na2SO4, and NiSO4 + Na2CO3 --> NiCO3 + Na2SO4.

Otwayites
Otwayite, Ni2CO3(OH)2, is a hydrated nickel carbonate mineral. Otwayite is green. Otwayite is found in association with nullaginite and hellyerite in the Otway nickel deposit. It is found in association with theoprastite, hellyerite, gaspeite and a suite of other nickel carbonate minerals in the Lord Brassey Mine, Tasmania. Otwayite is found in association with gaspeite, hellyerite and kambaldaite in the Widgie Townsite nickel gossan, Widgiemooltha, Western Australia. It is also reported from the Pafuri nickel deposit, South Africa.

Kambaldaites
Kambaldaite has the formula NaNi4(CO3)3(OH)3·3H2O.

Kambaldaite is an extremely rare hydrated sodium nickel carbonate mineral described from gossanous material associated with Kambalda type komatiitic nickel ore deposits at Kambalda, Western Australia, and Widgie Townsite nickel gossan, Widgiemooltha, Western Australia.

Kambaldaite is formed in the regolith as a supergene alteration mineral of nickel sulfide minerals, in arid or semi-arid environments which produce conditions amenable to concentration of calcareous or carbonate minerals in the weathering profile.

Kambaldaite is formed from a similar process to the weathering of other sulfide minerals to form carbonate minerals. The sulfide minerals which are weathered to produce kambaldaite are pentlandite, violarite, millerite and rarely nickeline.

Kambaldaite is associated with goethite, malachite, annabergite, gaspeite and magnesite in the nickel sulfide gossans of Kambalda and Widgiemooltha. It is not known from other nickel sulfide gossans within the Yilgarn Craton, potentially due to many of these existing within areas of laterite cover, deeper regolith development or less favorable rainfall conditions.

Kambaldaite is not reported from the Tasmanian or New South Wales nickel carbonate occurrences because it is a supergene carbonate mineral and not a hydrothermal mineral.

Zaratites
Zaratite is a bright emerald green nickel carbonate mineral. The formula for zaratite from Tasmania is Ni3CO3(OH)4·4H2O.

It is a rare secondary mineral formed by hydration or alteration of the primary nickel and iron bearing minerals, chromite, pentlandite, pyrrhotite, and millerite, during the serpentinization of ultramafic rocks. Hellyerite, NiCO3·6H2O, is a related mineral.

Basic nickel carbonate can be made by treating solutions of nickel sulfate with sodium carbonate, shown here for the basic carbonate:
 * 4 Ni2+ + CO32− + 6 OH− + 4 H2O → Ni4CO3(OH)6(H2O)4

Hellyerites
Hellyerite, NiCO3·6(H2O), is an hydrated nickel carbonate mineral, light blue to bright green in colour, has a hardness of 2.5, a vitreous luster, a white streak and crystallises in the monoclinic system. The crystal habit is as platy and mammillary encrustations on its matrix.

The environment of formation, associated only with metamorphosed ultramafic rocks, is diagnostic compared with gaspeite, another nickel carbonate which is associated with supergene weathering of nickel sulfide minerals.

Hellyerite is observed forming in shear planes in serpentinite, produced by carbonation of the serpentinite. Hellyerite forms in this environment in nickel rich serpentinites, which are metamorphosed equivalents of ultramafic cumulate rocks such as peridotite and dunite. Peridotite and dunite, when fresh, can contain up to ~4,000 ppm nickel within olivine.

Mineral alterations
Chalcopyrite CuFeS2 (primary) readily alters to the secondary minerals bornite Cu5FeS4, covellite CuS and brochantite Cu4SO4(OH)6.

Galena PbS (primary) alters to secondary anglesite PbSO4 and cerussite PbCO3.

Sphalerite ZnS (primary) alters to secondary hemimorphite Zn4Si2O7(OH)2.H2O, smithsonite ZnCO3 and manganese-bearing willemite Zn2SiO4.

Pyrite FeS2 (primary) alters to secondary melanterite FeSO4.7H2O.

If the original deposits contain arsenic and phosphorus bearing minerals secondary arsenates and phosphates will be formed.

Gaspéites
"Gaspéite's formula is (Ni,Fe,Mg)CO3 and it is a bright green mineral. It forms massive to reniform pappillary aggregates in fractures, bottryoidal concretions in laterite or fracture infill. It is also present as stains and patinas on iron oxide boxworks of gossanous material."

"Gaspéite is formed in the regolith as a supergene alteration mineral of nickel sulphide minerals, generally in arid or semi-arid environments which produce conditions amenable to concentration of calcareous or carbonate minerals in the weathering profile."

"Gaspéite from Widgiemooltha is associated with talc carbonated komatiite-associated nickel sulphide gossans and is probably formed by substitution of nickel into carbonates such as magnesite which are formed by oxidation of the talc-carbonate lithology, and of primary and supergene nickel sulphide minerals."

"Gaspéite is formed from a similar process to the weathering of other sulphide minerals to form carbonae minerals. The sulphide minerals which are weathered to produce gaspeite are pentlandite, violarite, millerite and rarely niccolite."

Hypogene processes
Def. formed "underground, often by ascending solutions" is called a hypogene process.

In ore deposit geology, hypogene processes occur deep below the earth's surface, and tend to form deposits of primary minerals, as opposed to supergene processes that occur at or near the surface, and tend to form secondary minerals.

At great depth the pressure is high, and water can remain liquid at temperatures well above 100 °C. Hot aqueous solutions originating in the magma contain metal and other ions derived from the magma itself, and also from leaching of surrounding rocks. Hypogene deposition processes include crystallization from the hot aqueous solutions rising through the earth's crust, driven by heat provided by the magma.

Major dissolved components are chlorine, sodium, calcium, magnesium and potassium, and other important components include iron, manganese, copper, zinc, lead, sulfur (as SO42− or S2− or both) carbon (as HCO3− and CO2) and nitrogen (as NH4). Most ore fluids contain chloride as the dominant anion.

As the solutions rise the temperature and pressure fall. Eventually a point is reached where the minerals start to crystallise out. Minerals formed in this way are called primary, or hypogene, minerals. Sulfur is a common component of the fluids, and most of the common ore metals, lead, zinc, copper, silver, molybdenum and mercury, occur chiefly as sulfide and sulfosalt minerals such as pyrite (FeS2), galena (PbS), sphalerite (ZnS), and chalcopyrite (CuFeS2).