Physico-chemical characterization of Ogun and Sokoto phosphate rocks

Abioye O Fayiga ,G O Obigbesan

doi:10.4314/gjpas.v23i1.4

Abstract

There is a need to identify potential phosphate rock sources to supply phosphorus (P) for crop growth and sustain food production. Physico-chemical characteristics of phosphate rocks from two Nigerian deposits were evaluated to determine their suitability for processing or direct application as P fertilizer. Physical properties such as textural forms, hardness, specific gravity, shrinkage, water absorption capacity and firing color were determined. Ogun rock phosphate (ORP) and Sokoto rock phosphate (SRP) were also subjected to chemical and mineralogical analysis. Solubility tests were conducted at two different particle sizes in 2% citric acid. ORP had a higher water absorption capacity and shrinkage than SRP while specific gravity of ORP was lower. Total P 2 O 5 of SRP and ORP were 36.1% and 31% respectively, which is greater than P 2 O 5 content of Morocco rock phosphate. Both ORP and SRP contained carbonate fluorapatite and chlorapatite minerals. Gypsum, calcite and lime were associated with both rock phosphates indicating their liming potential in the soil. ORP was more soluble in water, probably because it has a lower pH (5.0) than SRP (7.8). Higher solubility of SRP in 2% citric acid may be caused by its high carbonate content. Solubility of both rocks in 2% citric acid increased with decreasing particle size. Solubility of both rocks in 2% citric acid was greater than 30% indicating that they are reactive rocks. The agronomic effectiveness of these rocks has been validated in several on farm trials. We recommend these phosphate rocks for production of P fertilizers and direct application in crop production.

Highlights

Phosphate Rock (PR) is used in agriculture to produce fertilizer and animal feeds, in the industry for production of detergent or food additives, in energy industry as a source of uranium and rare earth metals, and in environmental science for metal immobilization (Ibrahim et al, 2010)
Ogun rock phosphate (ORP) exists in forms such as nodules, granules, pellets and vesicles while Sokoto rock phosphate (SRP) occurs as nodules and pellets (Plate 1)
SRP from the arid region of Nigeria had higher rock strength and was better preserved as pellets probably because it was not subjected to the high rainfall regime of the South Western part of the country where ORP is located

Summary

Introduction

Phosphate Rock (PR) is used in agriculture to produce fertilizer and animal feeds, in the industry for production of detergent or food additives, in energy industry as a source of uranium and rare earth metals, and in environmental science for metal immobilization (Ibrahim et al, 2010). Extensive deposits of phosphates occur in 4 sedimentary basins in Nigeria; Dahomey basin in Ogun state; Lullemeden basin in Sokoto state; Anambra basin in Imo state; Niger Delta basin in Edo state (Adegoke et al, 1994). Sokoto phosphates can be found in different forms; nodules and pellets in clays, shales and limestones; and primary phosphatic shales, limestones and siltstones (Adegoke et al, 1994)

Methods

Results

Discussion

Conclusion