Laboratory Formation and Characterization of Taranakite in a 
Hydrol Humic Latosol Soil from Hawaii 1 
Po-Ling Liu, G. D. Sherman, and L. D. Swindale 2 
ABSTRACT: The mineral taranakite was obtained in reactions between samples 
of an Akaka soil and monopotassium phosphate solutions ranging from 0.2 to 0.6 
molar, at pH values of the reacting system ranging from 2.3 to 2.9. Characteristics 
of the reaction products were compared with those of pure synthetic taranakite, 
using X-ray, chemical, optical, infrared absorption, and differential thermal tech- 
niques. 
The taranakite was essentially a potassium-aluminum-phosphate complex. There 
was no indication of isomorphous substitution of iron for aluminum. The molar 
ratios of K/P0 4 and A1/P0 4 of the reaction product were found to be 0.37 and 
0.72 respectively. The taranakite was thought to be formed by precipitation of a 
soluble phospho-alumino complex anion together with potassium ions. 
The possibility is suggested of the formation of taranakite when soluble potas- 
sium and phosphate react with Hydrol Humic and Humic Latosols in the field. 
During the early stages of reaction, the reaction product is believed to be crypto- 
crystalline, but the size of crystals increases with time. 
In Hawaiian soils large amounts of added 
phosphate often are rendered at least tempo- 
rarily unavailable to plants. Davis (1935) at- 
tributed this phenomenon to an absorption ef- 
fect in the soils. He found that, for any given 
equilibrium phosphate concentration, the 
amount of phosphate fixed varies directly with 
the ratio of soil to solution. Chu and Sherman 
(1952) reported that, in the presence of hy- 
drated iron and aluminum oxides, as much as 
90% of added soluble phosphate was fixed by 
the soils in a relatively short period of time. 
When the oxides were removed, less than 30% 
of the applied phosphorus was fixed. The Hy- 
1 This paper is a joint publication of the Hawaii 
Agricultural Experiment Station and the Hawaii In- 
stitute of Geophysics. It is published with the ap- 
proval of the Director, Hawaii Agricultural Experi- 
ment Station, as Technical Paper No. 739, and with 
the approval of the Director, Hawaii Institute of 
Geophysics, as Contribution No. 151. It is a 
portion of a thesis submitted by the senior author to 
the Graduate School, University of Hawaii, in partial 
fulfillment of the requirements for a Master’s degree 
in Soil Science, January, 1965. Manuscript received 
April 1, 1965. 
2 Department of Agronomy and Soil Science, Col- 
lege of Tropical Agriculture, University of Hawaii, 
Honolulu, Hawaii. 
drol Humic Latosols showed the highest phos- 
phorus-fixing capacities, but the Low Humic 
Latosols and Humic Latosols also fixed phos- 
phorus to a considerable extent. 
The manner in which phosphate is fixed in 
acid soils is as yet unknown, but in some in- 
stances it is likely to be in the nature of a solu- 
tion-precipitation. Kittrick and Jackson (1955) 
reported, from electron microscope observations, 
that a solution-precipitation mechanism was 
operative in the reaction of phosphate with 
colloidal iron oxide particles and thin aluminum 
hydroxide films at room temperature. These 
authors also reported (1956) that there is a 
solution-precipitation mechanism operative in 
the reaction of phosphate with kaolinite and 
greenalite at room temperature. The reaction 
product in the potassium phosphate-kaolinite 
system was taranakite. 
Several workers have identified phosphate 
complexes which could occur as reaction prod- 
ucts in hydrous colloidal sesquioxide systems 
(Wada, 1959; Birreil, 1961; Lindsay et ah, 
1962; Tamimi et ah, 1963; Tamimi, 1964). 
These phospho-reaction products have been as- 
sociated with the presence of calcium, ammo- 
nium, and potassium cations in the system. 
496 
