• Bert Quin

The History of RPR in NZ

There was a time (in the 1990s and early 2000s) when farmers were spoilt for choice with RPR. Summit-Quinphos offered Gafsa RPR from Tunisia and Kosseir RPR from the Red Sea Coast of Egypt; other companies offered Sechura from Peru. The superphosphate industry sold medium-reactivity (at best) phosphate rock from Morocco as an RPR until they got caught out two years ago and changed to calling it a ‘DAPR’ (direct application phosphate rock), and even got the buyer so sign a declaration to say that they knew it wasn’t the real McCoy. Unbelievable!

So what is available on the New Zealand and Australian market today? I have been having a look at what is going on and am not impressed! In New Zealand, the message and efforts of a few small private companies is being swamped by what I believe is deliberate disinformation and misinformation coming from the Big 2, who I think are, with some justification, afraid of the implications for superphosphate manufacture in New Zealand if true RPRs become widely available and better promoted, as they were up until a decade ago. The environmental advantages of switching to RPR for maintenance are huge.

As a result, I have decided to get back into true RPR importing – at the wholesaler level – and provide reputable companies with a product that has my full confidence and support. This RPR I have selected comes from the ‘Djelbel Onk’ area of the Algerian RPR deposit. This is a truly massive RPR deposit – quite possibly the biggest in the world – and has the ideal combination of characteristics. It has a good total P level of 12.7%, 30-30.5% average citric solubility, and only 18 ppm Cd (which equates to only 140 micrograms Cd per kg of P, only half what the NZ industry regards as an acceptable limit.

NB: Note that because the Algerian RPR has a vein (1-3m thick) of phosphatic dolomite running through it, depending on where a particular sample of RPR was taken, the dolomite can range from 3-7%. At its minimum, the citsol is about 35%, at its maximum, the citsol can be only 28%. Either way, this has NO EFFECT on its effectiveness as an RPR fertiliser (apart from supplying extra Mg for free at the top end). The effectiveness comes from the geological and geochemical makeup of the RPR itself, NOT from some outdated, el-cheapo, easy-to-manipulate 30-minute citric acid test. 

I would like to fill in a bit of the background story here, so bear with me!

The Tunisian RPR (which Summit-Quinphos used to import, along with Egyptian Kosseir) is actually an extension of the Algerian deposit. Unfortunately for the Tunisians, on their side of the border, the deposit increases rapidly in cadmium (Cd) content as it gets further into Tunisia, from about 20ppm at the border with Algeria to about 80ppm at the eastern end of the deposit. In those days, I insisted that we received product from close to the Algerian border, with a maximum of 25ppm, equivalent to under 200 micrograms of Cd per kg of P, a bit higher than the Egyptian’s 12-15 ppm but still much lower than the industry’s self-imposed limit.

At the time, Sumotomo Corporation – who owned most of Summit-Quinphos – would not let me go to Algeria, because it was considered too risky for kidnapping of overseas business executives. Well, what a change a decade makes! Algeria sailed through the ‘Arab spring’ of a few years ago with little or no disturbance,  and it has a relatively stable government and steadily improving economy, phosphate and other exports and overseas investment. I used to meet with their senior fertiliser executives at international conferences, and told them that one day I would find a way to start exporting their product. So finally, the opportunity to represent the Algerian RPR in NZ has come about!

Unlike some self-appointed ‘experts’ on RPR, I make very sure I visit all the deposits themselves, so that I truly understand not just the geology and  geochemistry of the deposit, and just as importantly, the mining operation and beneficiation capabilities and options.

It continues to amaze me how many soil fertility scientists still refer to all RPR deposits by country alone, as though somehow all the RPR or even phosphate rock in general within a given country is the same! It illustrates the arrogance of ignorance, and a total lack of respect for other scientific disciplines outside their own, particularly geochemistry and geology. I consider myself fortunate that I was able to include some of both in my university studies.

It has recently been determined that the Algerian RPR deposit near Djebel Onk is probably the biggest, and one of the most homogeneous, RPR deposits known. It exists of one very deep layer of 25-30m  covering a large area. Its variation is very small, being affected only by a 2m-thick layer of dolomitic phosphate that runs through it at variable depth. This dolomite content  can be as high as 10% in some depths of the deposit, but averages about 6-8% in a typical days production of 10,000 tonnes. Since the installation of a new mineface and beneficiation plant 2 years ago (following an earthquake), the amount of dolomite present can be varied a bit  to a during  mining the beneficiation process. This is important,  because although dolomite is beneficial agronomically for NZ farmers and many others,  it reduces the P content slightly by dilution (only slightly, because the dolomite has P in it as well.

Another significant but purely semantic point is that the presence of dolomite artificially reduces the citric solubility as measured in the standard citric acid solubility test. At the maximum 10% dolomite content, the dolomite in the RPR quickly consumes most of the citric acid in the test, increasing the pH of the citric acid solution from 2.2 to 3.2, and thereby reducing the measured ‘citsol’ from 31% to about 27%. This does not adversely affect its agronomic performance in the field at all, but  I decided to go with a bit less less dolomite. Funnily enough, Summit-Quinphos came across the same issue with Egyptian Red Sea RPRs way back in the early 1990s. The Hamrawein deposit contained free dolomite, but the Kossier did not, so we switched to the Kossier. I think the Hamrawein and Algerian deposits are the only two that contain significant dolomite mixed with the RPR. Another well-established example is NZ’s own under-sea deposit, the Chatham Rise phosphorite nodules. These come with 30% calcite (lime) in the nodules, reducing the total P content to only 9%, and reducing the initial citric solubility test to only 15%. Despite this, in all comparisons, it has performed as well as other RPRs. So has Algerian RPR.

The Algerian phosphate mining company (Somiphos, a subsiduary of Ferphos) make two particle size grades; a finer grade for use as an RPR, and a coarser grade sold for the manufacture of phosphoric acid and high analysis fertilisers. In these, the manufacturer is grinding the rock to a very fine powder before treatment with concentrated sulphuric acid, so there is no need for Somiphos to grind it as finely themselves.

That is the end of my digression, so let’s get back to other RPRs (and psuedo RPRs) available in NZ.

My biggest concern by far is what has become the common practice in NZ of misusing the atypically high citric solubility of Sechura RPR (40%) by mixing it say 50/50 or 70/30 with much lower quality phosphate rocks such as those from Morocco, knowing the citric solubility of the mix will still be 30% or above. It might still have 13%P, but its agronomic peformance will be be greatly reduced. As my father Frank Quin used to say, you can’t put wings on a chicken and expect it to fly like a eagle! It is abusing both farmers and the Sechura RPR itself to do this.

The practice of blending Sechura RPR with other phosphate rocks is also done to get a lower cadmium (Cd) analysis by blending it with a lower Cd content phosphate rock, again usually Moroccan. The Cd content of the 8 layers that make up the Sechura deposit range from 20 up to 50 ppm. I know this because of extensive consultancy work I did there for an international mining company. Unfortunately, the low Cd layers are at the bottom, and it is totally uneconomic to selectively mine them. The best you can achieve with the mining and beneficiation available in Peru, without calcining the RPR at high temperature to drive off some of the Cd into the atmosphere, is  about 38 ppm, or 290 mg Cd/kg P. With costly calcination you can get the Cd down to 33 ppm (250 mg Cd/kg P), but the reactivity is greatly reduced in the process. This is fine if you are using the phosphate rock to manufacture soluble fertiliser, but for direct use as an RPR that’s a no-no. One manufacturer is believed to have made this rather basic mistake quite recently.

So, if you are buying what you are told is Sechura RPR, it should have at least 40% citric solubility, and it will have about 38ppm Cd. If either of these figures are lower than this, it is not true Sechura RPR, so beware. The only exception to this is the small quantities of completely unbeneficiated Sechura RPR brought in by one or two companies from time to time. Because it still contains the clay and silt, it contains only 9-10% P, not 13%, so beware even more. The Cd will be about 25-30 ppm Cd (260-300 mg Cd/kg P), depending on the Cd content of the clay and silt. Some of the this clay contains just as much Cd as the RPR itself!

You should be asking how on earth we can avoid these shenanigins. Well the good news is that it can be achieved by Fertmark imposing two, preferably 3,  quite simple requirements.  Firstly, the importer and retailer must both submit declarations stating the exact mining origins and percentages of all significant mineral components of any product they sell that is claimed to be an RPR. Secondly, samples need to be analysed for their crystal a-axis measurement by the International Fertilizer Development Centre in Alabama, USA. This test is very difficult to fake, which is I suspect why there is resistance to adopting it from some quarters in NZ. Thirdly, and most importantly, dump the current 30-min citric acid test, which is as said is far, far too easy to manipulate and therefore way beyond its use-by date, and replace it with the far better  4-stage or 5-stage  sequential citric solubility test. It’s time for Fertmark to stand up and refuse to let the reputation of true RPR be undermined. It is simply too important to NZ farming and the environment not to do this.