Abstract
The precipitation of basic nickel carbonate hydrates was studied from nickel sulphate solutions (concentrations 0.05 M to 1 M) at 96Β°C, by addition of sodium carbonate, bicarbonateβcarbonate and bicarbonate solutions. Precipitate compositions were determined by chemical analysis, thermogravimetric analysis, differential calorimetry and i.r. spectrophotometry; approximate final crystallite sizes and numbers were estimated from combined sedimentation and porosity measurements on precipitate aggregates.
Nucleation, and then crystal growth, started after some βcritical __p__Hβ pH = 7.05 to 7.67 (at CO~3~^ββ^/Ni^++^ ratio = 0.08β0.12); the solution __p__H then remained constant (until the CO~3~^ββ^/Ni^++^ ratio = 0.8) and then rose to some final value. Nucleus numbers, and thence final crystallite numbers, decreased with increasing bicarbonate content of the precipitating solution and decreasing pH.
Precipitate compositions did not vary significantly with reacting ion concentrations but the Ni(OH)~2~/NiCO~3~ ratios decreased from 2 to 1.4 with decreasing pH: thermal analysis and i.r. spectrophotometry confirmed that the final precipitates were mixtures of olated nickel carbonates and not nickel carbonateβnickel hydroxide mixtures.
Final crystallite sizes of the precipitates from 1 M solutions varied approximately from 0.095 to 0.14 micron, for the above __p__H range.